The smartly dressed sales executive travelling on the number 96 bus across Leeds didn't notice his body descending into a state of severe hypoglycaemia.

Amnesty International says 334 people in the US died between 2001 and 2008 after the stun guns were used on them. Taser International, the Arizona-based manufacturer, dismisses these findings. (Christopher Furlong/Getty Images) He didn't have time to ask his fellow passengers for help, or press the bell. Instead he slumped back in his seat in a diabetic coma, his head lolling from side to side.

This was why he wore a special tag and chain around his neck: it advertised his diabetes. His mother and father, both retired GPs, had encouraged their son to wear it ever since he had started having to take insulin 20 years earlier.

Nicholas Gaubert had been looking forward to a drink with friends in the suburb of Headingley after work. Instead he was critically ill, unconscious on the top deck of a bus continuing its route north through the early evening rush-hour traffic.

Some 40 minutes later, it terminated at the Holt Park depot and the driver checked his vehicle. He was used to turfing drunks off the night bus at weekends, but it was Wednesday and the man apparently fast asleep on the top deck was far from dishevelled.

On another evening, the driver may have reacted differently, but the timing tonight was bad for Gaubert: just six days after the July 7, 2005 London bombings and one week before the fatal shooting of the Brazilian Jean Charles de Menezes by police firearms officers. Paranoia and suspicion, especially on public transport, were rife. And Gaubert had a rucksack.

So the driver kept his distance and shouted at him to wake up and leave. When Gaubert failed to stir, the driver climbed off the bus and told his superiors, who cleared the depot and called the police.

The nearby Asda supermarket was evacuated and an armed unit was called. Eight firearms officers were sent; three entered the bus. The white male didn't look like a textbook terrorist and the bus was empty and far from the city centre.

But he was sweating profusely, wouldn't respond to their shouted orders and they couldn't see his hands, so an officer pulled his X26 Taser stun gun out of its holster, flicked on the 50,000-volt electric gun's red dot laser sighter and pointed it at him. It was the first time a West Yorkshire officer had deployed a Taser.

The man was well within the 21ft range so, when he still failed to respond, the officer shouted a final warning and squeezed the trigger.

Two 20mm-long metal barbs attached to plastic-coated copper wires shot instantly and noiselessly from the barrel. The barbs penetrated Gaubert's cotton shirt and embedded themselves in his skin.

For five seconds there was a crackling noise as the electricity shot down the wires and discharged into his body. Gaubert's body went into uncontrollable muscle spasms and he fell from his seat.

He landed face down on the floor with one hand under his body. The police shouted again for him to show his hands but he still didn't move; so the officer pulled the trigger for a second time.

Another wave of electricity surged down the copper wires and tore into him. (At the subsequent inquiry, the officers would claim they had to stun Gaubert again to make sure it was safe to approach him).

Finally they got hold of him, put on handcuffs and put him into the back of a police van - which is when he regained consciousness and was able to shout that he needed urgent medical attention. He was taken to Leeds General Infirmary.

'I shudder to think what could have happened if I hadn't come round,' says Gaubert. 'They would have put me in a cell and I would probably have died. I was in a diabetic coma, and all they were bothered about was whether I was going to blow up an empty, stationary bus.

'I showed no aggression - I was unconscious and unable to respond to their demands. I think they just saw it as an opportunity to try out their toys.'

Gaubert has since become what is believed to be the first person in the UK to obtain compensation for being shot with a Taser.

West Yorkshire Police has confirmed that it made an out-of-court settlement - thought to be tens of thousands of pounds - and an apology, after a civil action brought against them.

No such apology was received by the 89-year-old war veteran who last year became the oldest person in the UK to be stunned with a Taser.

Three weeks before this incident, the retired carpenter had gone into a residential home for the elderly in Llandudno, North Wales. But the confused man, who has not been named, was determined to return to his family home, just a few minutes' walk away.

As the sun rose on a chilly Saturday morning in January he climbed out of a window at the care home and wandered the empty residential streets clutching a shard of glass. At 6.30am a police officer knocked him to the ground with a 50,000-volt Taser charge.

North Wales police later said their officers feared he would commit suicide using the broken glass. But the pensioner's sister-in-law told Live: 'He was frightened to death and was hiding behind cars. He told us that he held a piece of glass to his throat because he was afraid of the police - he wanted to keep them away.

'He said afterwards: "I would never have cut my throat." And that when he was hit by the Taser the pain was terrible.

'He fell to the floor and was handcuffed. It's awful that the police should end up shooting an old gentleman of his age.'

His daughter-in-law adds: 'They treated him like an animal. They should have talked him out of it. That's what they would have done in the past: talked to him, not shot him.' The family complained, but the Independent Police Complaints Commission backed the decision to use the Taser.

In most cases it is enough for an officer to draw the Taser out of its holster or to point the laser red dot at the offender to gain control.

On other occasions officers intimidate a target by switching on the electricity so the end of the weapon sparks - known as 'arcing'.

But Tasers were fired, or as police chiefs prefer to call it 'deployed', 1,765 times between April 2004 and June 2009. Stun gun officers have a less PC term for firing their weapon - they call it 'sparking up'.

Since being introduced in April 2004 Tasers have been used in more than 5,400 incidents in England and Wales.

The number of people being targeted is increasing all the time, and their use can now only rise further since the decision in 2008 by then Home Secretary Jacqui Smith to fund an extra 10,000 Taser guns.

Up to 30,000 front-line officers will be armed with the new weapons. Some forces will only let fully trained officers use them, but many will give them to officers after 18 hours' training.

Amnesty International says 334 people in the US died between 2001 and 2008 after the stun guns were used on them. Taser International, the Arizona-based manufacturer, dismisses these findings.

A spokesman claims: 'In only a couple of disputed cases has a Taser been listed as the "cause" of death.'

Nonetheless, Taser International issued guidelines last October warning police to avoid shooting a suspect in the chest 'where possible', and acknowledging the heart-attack risk from stun guns, although they still claim the danger is 'extremely low'.

But perhaps of greater concern than increased numbers of X26 guns is the expectation that the police will soon be armed with a new long-range model. The more powerful weapon can immobilise a suspect for 20 seconds from 100ft away and is being tested by Home Office scientists.

The eXtended Range Electronic Projectile (XREP), the size of a shotgun cartridge, is designed to pierce the target's skin and then deliver a 500-volt shock from its battery-powered circuits (the lesser voltage makes no difference to the pain and paralysing effect). Senior officers believe the XREP could be used in riots and other serious public order confrontations.

The Home Office says the new weapon is still under consideration, but a police source told Live: 'It is not a question of if, but when we get the go-ahead on this. This is an extremely useful bit of kit.'

The XREP round has three fins that pop out as it rotates through the air to increase its accuracy. It is fronted by four barbs designed to pierce clothing and skin, securing the projectile to the target's body. Six more electrodes fan out at point of impact, distributing the shock over a greater body area than the X26.

It can be fired from any 12-gauge shotgun, but Taser has developed a custom-designed shotgun, in conjunction with American firearms company Mossberg.

It uses 'ammunition key' technology to prevent accidentally using normal shotgun cartridges, and comes with a distinctive yellow stock and forearm. There is also a special mount that allows a Taser X26 to be attached to the underside of the barrel, so police could carry both weapons at the same time.

The possibility of this very different kind of Taser weapon coming into widespread use has provoked great concern among human rights organisations.

Oliver Sprague, the UK's Arms Programme Director of Amnesty International, says: 'Because it's a projectile weapon it's much more likely to cause injury and damage if it hits someone in the face or head.'

He adds: 'The key concern, however, is instead of Tasers being used in genuinely life-threatening cases, you start to see it creep into mainstream policing. It is disturbing to consider that a Taser could be in the hands of every police officer in a matter of years.'

'I'm walking down a long room in the dark. I know there's a violent thug lurking somewhere in the shadows; I've been warned. It's nerve-racking, even though I'm armed with a Taser.

'Suddenly a huge man wearing a motorcycle helmet leaps out in front of me. He starts slamming a baseball bat on the ground and shouting threats. My heart goes into overdrive.

'I manage to pull my stun gun out of its holster and turn it on, all without electrocuting myself. The red target dot is pointed at the centre of the hooligan's chest, and I shout a warning. I'm ignored. So I pull the trigger.

'What happens next reminds me of firing an old-fashioned spud gun; there is hardly any resistance or noise. The lightweight weapon looks and feels like an item from Lego's Star Wars range, but the comparisons with child's play end there.

'The metal prongs shoot out too fast to see. Amazingly, they are on target and lodge into my target's chest. For five seconds there's a crackling noise as the electricity flows and I yell 'Taser! Taser! Taser!'

The burst of 50,000 volts is automatically sent down the wires, but this shock can be repeated at the pull of the trigger. The Taser can also be held against a person and the electric charge activated. This is known by officers as a 'drive-stun'.

Because this is a Metropolitan Police Taser refresher training day in west London, my would-be assailant, who is now lying flat on his back, is heavily padded and wearing a protective vest.

Pulling the trigger felt like a no-brainer, but in real life most encounters involving Tasers are nowhere near as straightforward, and require officers to think fast under pressure.

Critics do acknowledge that, when used properly, the Taser provides the police with an invaluable addition to their arsenal.

The weapon has undoubtedly saved lives, prevented hundreds of serious injuries to both the police and suspects and reduced the number of times officers have had to open fire with more deadly conventional handguns and semi-automatic rifles. They have also proved an effective deterrent against violent offenders.

Sergeant Andy Harding is the Met's Territorial Support Group's lead Taser instructor and a national police stun gun adviser.

He says, 'A few years ago you would have had doors being splintered, hand-to-hand fighting, and people getting injured.

'The huge difference now is that you don't need to get up close and personal. People are aware of what a Taser can do and are terrified of the red dot.'

But while the Metropolitan Police's TSG public order unit has won plaudits from around the world for their Taser training and deployment, there is growing concern that other British police forces and squads are far less stringent when it comes to using the weapons.

National police guidelines state that a Taser should only be used in situations where an officer is 'facing violence or threats of violence of such severity that they would need to use force to protect the public, themselves or the subject.'

There also appear to be alarming differences between police forces as to how guidelines are interpreted. You might think London's Metropolitan Police, as the biggest force in England and Wales, should logically be the 'Taser capital' of Britain. But the title goes to a force 250 miles north - Northumbria.

Despite having only 4,100 officers (compared with the Met's 32,600) Northumbria comes top of the Taser league table, having used a Taser 797 times from April 2004 to June 2009, compared with 751 by the Met.

Third place goes to West Yorkshire with 378. Comparisons with other forces further highlight this Taser postcode lottery. For example, in Merseyside, whose police force is slightly bigger than Northumbria, Tasers have only been used 80 times since April 2004.

And as Live has discovered, not only are they being used more often, but increasingly police forces are deploying them against children.

Records obtained using Freedom of Information requests show that the police in England and Wales fired or threaten to fire Tasers against at least 142 under-18s in the 20 months up to the end of August 2009.

The youngest case disclosed involved a 12-year-old boy who was threatened with a Taser after West Mercia police were called to a school in Kidderminster in February 2008. The boy had threatened staff with a pair of scissors. After officers with Tasers were deployed he surrendered his weapon and was arrested.

Northumbria officers used Tasers against under-18s 33 times, including stunning four 16-year-olds and a 15-year-old, in the 20 months up to August 2009.

This compares with 24 incidents in the Met during the same period. North Wales Police Tasered three 16-year-olds in the first eight months of 2009; the force will reveal only that the incidents involved boys 'threatening self harm'.

In another incident in North Wales in February 2008 an officer Tasered a 15 year-old boy who was smashing up furniture at his home in Gwynedd.

Experts warn against Taser use on children because of the risk of a heart attack. The Government advisory body, the Defence Scientific Advisory Council, notes 'children and adults of small stature [are] at potentially greater risk from the cardiac effects of Taser currents than normal adults of average or large statue.'

National police guidance stresses that officers should be 'vigilant' in considering whether to stun a child or small person.

But a Home Office spokeswoman counters: 'The latest statement from independent medical advisors states that the risk of death or serious injury from the use of Tasers is very low.'

America, by virtue of its numbers and longer experience, has the most extreme anecdotes about Tasers. One of the most disturbing incidents took place last November, after local police were called to a home in Ozark, near Little Rock, Arkansas, to investigate a reported domestic-disturbance.

According to the report by Sheriff Dustin Bradshaw, when he arrived, a ten-year-old girl was curled up on the floor and screaming.

The officer wrote in his official report: 'Her mother told me to "Tase" her if I needed to.' The officer tried to take the girl, who has emotional problems, into custody. But she was 'violently kicking and verbally combative' and kicked him in the groin.

So Sheriff Bradshaw delivered 'a very brief drive stun to her back,' his report said. The girl's father didn't approve of his daughter being shocked with 50,000 volts.

Anthony Medlock told a local newspaper: 'My daughter doesn't deserve to be Tasered.' No disciplinary action is to be taken against the officer after his boss defended his action.

Liberal Democrat shadow home secretary Chris Huhne believes the UK should learn from the US experience of Tasers.

He says: 'Given the serious concerns about the safety of Tasers, which have killed more than 300 people in the US, they should not be used on children.

'Ministers should not be putting Tasers in the hands of any more police officers until they really know how dangerous they are. A full inquiry into their use must be conducted before they are rolled out any further.'

Not all forces agree with the decision to arm nonspecialist officers. Sussex Police and the Metropolitan Police are among those which are refusing to extend the use of Tasers to the rank and file. Northumbria Police, however, defends its use of the weapons.

Assistant Chief Constable Steve Ashman says, 'Far from endangering the public I would contest that such usage of this tool has resulted in less risk to the public and police officers alike.'

This positive view is not one shared by Nicholas Gaubert, who accused police of using him for 'target practice' when they stunned him twice while he was unconscious in a diabetic coma.

Gaubert's solicitor Ifti Manzoor is equally scathing: 'The question remains - why didn't it cross the police's mind that this man might be ill? Instead they opted to hit an innocent man with 50,000 volts. My client believes he is fortunate to still be alive.'

With increasing numbers of guns, the danger of them being used as a first resort and the potential arrival of a powerful new weapon, fears will only grow that too often the response appears to be to stun first, ask questions later.