News that the US government is in the process of constructing an international "wanted" database to share biometric information on a grand scale should be treated with caution. Biometrics - including DNA and fingerprints - are a vital weapon in the fight against crime. And cross-border crime is a growing problem. I am determined that Britain should work with our allies, in Europe and beyond, to defeat it. But giant databases that don't have adequate privacy protection systems are not the right way forward.The details of how the US system will operate are still opaque. They may bring forward proposals we should support.

But I won't be holding my breath. It is typical of the US administration to go for overkill: giant solutions that sound great on paper but are based on unproven and even unworkable technologies. The "son of Star Wars" anti-ballistic missile system, which would attempt to shoot down incoming missiles, is a case in point. It's cost billions but not only does it anger countries like Russia, it doesn't even work.

Unfortunately, it is also typical of the UK government to doff its cap and sign up to any idea that emerges from Washington, however kooky. We're signed up to son of Star Wars. I expect we'll be signed up the FBI's "Server in the Sky" too, whether it's the right thing to do or not.

Biometrics are invaluable, but they are not 100% failsafe: nothing is. Remember: it's the US terrorism operations that put Yusuf Islam (the musician formerly known as Cat Stevens) on a "no-fly" list.

And once data is in the hands of the US authorities, there is no getting it back. We already send them massive amounts of information about air passengers, through a deal brokered by the European Commission, without any guarantee it will be properly safeguarded once it reaches the US. It would be foolhardy to start sharing further information without a simple guarantee: that data collected under UK law should continue to be protected even after it leaves Britain.

We should share information when other countries can guarantee data protection standards that match, or exceed our own. Otherwise, who knows which one of us will be on the no-fly list next.

Nick Clegg is the Liberal Democrats' home affairs spokesman.

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