Daniel Sylvester can't forget the night the police fired 50,000 volts of electricity into his skull. The 46-year-old grandfather owns his own security business, and he was recently walking down the street when a police van screeched up to him.

He didn't know what they wanted, but obeyed when they told him to approach slowly. "I then had this incredible jolt of pain on the back of my head," he explains. The electricity made him spasm; as he fell to the ground, he felt his teeth scatter on the tarmac and his bowels open. "Then they shot me again in the head. I can't describe the pain." (Another victim says it is "like someone reached into my body to rip my muscles apart with a fork.") The police then saw he was not the person they were looking for, said he was free to go, and drove off.

This did not happen in Egypt or Saudi Arabia or any other country notorious for using electro-shock weapons. It happened in north London and, if the Home Secretary, Jacqui Smith, has her way, it will be coming soon to a street near you. In Britain there are 3,000 police officers trained to use Tasers as part of specialised armed response units, but Smith has fired a jolt forward. She wants there to be 30,000 Taser-carrying officers, authorised to use them against unarmed citizens, including children. These "stun-guns" fire small metal darts into your skin, and through the trailing wires run an agonising electric current through your body.

Smith is right to say that the police face a growing threat of violence, and these heroic frontline officers must have the means to defend themselves. She's also right to argue it better to use a Taser than to use a gun. But the police can already swiftly call out armed response teams, equipped with Tasers and firearms. If we move beyond this to a widespread culture of assault by electricity, it will only endanger the police - and the rest of us.

Smith wants Tasers to be distributed well beyond the ranks of specially trained firearms officers, but Tasers can kill. Amnesty International has just published a report showing that, since 2001, 334 people have died in the US during or just after Tasering. Jarrel Gray was a partially deaf 20-year-old black man involved in an argument in the street in Frederick County, Maryland, when the police approached him and ordered him to lie on the ground. He didn't hear them - so they Tasered him. As he lay paralysed on the ground, they told him to show his hands. He couldn't obey. They Tasered him again. Jarrel died in hospital two hours later.

Ryan Rich was a 33-year-old medical doctor who had an epileptic seizure while driving his car on a Nevada highway. He crashed into the side of the road. The police smashed a window to get into the car and Ryan woke up, startled. The police officer reacted by Tasering him repeatedly. Only when they were handcuffing him did they notice he was turning blue. He was dead before he got to hospital. The coroner noted dryly that the Taser "probably contributed" to his death. Taser International's brochures claim their weapons have "no after-effects."

There may, in fact, be even more deaths than are recorded. Taser International has responded to medical examiners saying their weapons kill not by changing their weapons, but by suing the medical examiners. After the chief medical examiner of Summit Country, Ohio, ruled that Tasering caused the death of three young men, they sued her, and she was forced to remove the conclusions from her reports. The president of the National Association of Medical Examiners says Taser International's behaviour is "dangerously close to intimidation".

Yet Smith appears still to be taking the corporate propaganda of Taser International - who dominate the international stun-gun market - at face value. The company are startlingly glib when their spiel begins to crumble. A recent scientific study conducted by biomedical engineers for the Canadian Broadcasting Corporation found that nine per cent of the guns give a far larger electric shock than advertised. Some sent a 58 per cent higher voltage through the victim's body. Steve Tuttle, the vice-president of Taser, responded: "Regardless of whether or not the anomaly is accurate, it has no bearing on safety." The UK Defence Scientific Advisory Council has warned there is research suggesting that Tasers could cause "a serious cardiac event" when fired at children. But still Smith won't compromise.

Everyday on-the-beat policing does n0t happen in the tightly controlled scenarios imagined by the Home Office. It is messy and scrappy and carried out at high speed by people who are frightened and coursing with adrenaline: some 90 per cent of Tasered people in the US are unarmed. Matthew Fogg, who led a SWAT team in the US, warns that Tasers create a culture where "if I don't like you, I can torture you".

If we slip into that policing culture, mistrust and violence against police officers can only increase. That's why so many senior police are highly sceptical about Smith's plans, from the former head of the Flying Squad, John O'Connor, to the former head of the West Midlands Police, Barry Mason.

Far from lowering violence, Tasers seem to lower the threshold that by which the police resort to violence - and criminals respond by lowering theirs. In the US, a 16-year-old schoolboy was Tasered by cops in a playground for "using profanity"; a dementia-riddled man in his eighties was shocked for urinating in the park; 50,000 volts were fired at a 17-year-old boy who had fallen off an overpass and broken his back.

The Metropolitan Police have said they won't participate in Smith's Taser roll-out because they know it'll be particularly disastrous for relations with black and Asian communities. In the US, only 18 per cent of Tasered people are white. Imagine if the boys in Brixton and Moss Side weren't just been stopped-and-searched - which creates enough grievance - but apprehended in this way. How many Taser attacks would have to make it onto YouTube before we have riots?

Daniel Sylvester still has nightmares about what happened to him. If we don't stop Jacqui Smith, many more British people will be joining him - and we will all be in for a shock.