The Tories have moved to sabotage the Government's national identity card scheme a year before its launch.
The party was accused of "political point-scoring" after it wrote to Sir Gus O'Donnell, the Cabinet Secretary, giving formal notice that an incoming Conservative government would scrap the project.
It has also warned firms bidding to run the ID card scheme that their contracts would be cancelled shortly after a Tory election win.
Under Home Office plans, the first biometric identity cards will be issued to non-European foreign nationals next year. Britons would begin to receive their cards when they renew their passports the following year, with "significant volumes" being sent out in 2010.
With the next election expected in 2009 or 2010, the Tory moves could further destabilise the already troubled project, which has suffered a series of delays as well as protests over its impact on civil liberties.
David Davis, the shadow Home Secretary, challenged Sir Gus to guarantee that the taxpayer would not be hugely out of pocket if the ID scheme was scrapped.
He said: "As a matter of financial prudence, it is incumbent upon you to ensure public money is not wasted, and contractual obligations are not incurred, investing in a scheme with such a high risk of not being implemented.
"In particular, I would be interested to know what provision, if any, has been made in the relevant contractual arrangements to protect the Government - and public funds - against the costs that would be incurred as a result of early cancellation of the scheme."
In a letter to firms expected to be involved, Mr Davis warned of the "commercial risks involved" of bidding to run the scheme.
He said: "Your company may wish to consider carefully the financial viability of any contract, with the present Government, to participate in this project."
The Tories will launch a campaign today, including leaflet and poster advertising, against ID cards. They are encouraging voters to sign a national petition against the scheme.
John Reid, the Home Secretary, said ID cards would help secure Britain's borders, boost the fight against illegal immigration, combat people-trafficking and protect the country against terrorism.
He said: "The Tories' ill-considered opposition highlights their lack of leadership on security issues - they can't be trusted with Britain's safety. David Davis has shown that he and David Cameron talk tough while acting soft. They are more interested in political point-scoring than backing Labour's tough and necessary measures to keep the country safe."
The Government finally secured parliamentary backing last March for the ID scheme, which will cost £5.4 billion over 10 years.
Mr Davis said: "There are many other more worthwhile things the money could be spent on such as a dedicated UK Border Police or more prison spaces. People would much rather that their money was spent on these kind of schemes than being wasted on a plastic poll tax."Reuse content