Two of Britain's leading civil liberties groups are to offer a £1,000 reward for the fingerprints of the Prime Minister or Home Secretary - a move that could leave both groups open to prosecution for incitement.

The anti-ID cards group No2ID and the campaign organisation Privacy International will this week take out spoof 'Wanted' posters in tube stations and pub lavatories offering the cash to anyone who can lawfully obtain either the fingerprints of Gordon Brown or Jacqui Smith. An initial print run of 10,000 has been commissioned.

The posters, resembling those issued by US sheriffs hunting outlaws in the Wild West, are backed by an internet campaign and accuse Brown and Smith of 'identity theft'. They stipulate that 'the fingerprint must be obtained lawfully and can be located on a beer glass, doorknob or any object with a hard surface. Corroborating evidence is required to ascertain the identity of these thieves.' The £1,000 reward will then be paid to the charity of the 'bounty hunter's choice', as the posters put it. The poster continues: 'As fingerprint technology spreads, this government will essentially have back-door access to your computers, files, wallets and even cars and homes. We are offering this bounty to teach these individuals a lesson about personal information security.'

Phil Booth, of No2ID, said the campaign was designed to highlight the increasing sensitivity of fingerprinting as a political issue. 'Having committed the largest data breach in history, the government is about to perpetrate the largest identity theft in history,' he said.

'I'm sure the government will seek legal advice to see if we can be prosecuted,' said Simon Davies, director of Privacy International. 'But it would be a foolish government that would try to charge civil rights groups.'