Amid signs of further delay, the Conservatives have said that the government's identity cards scheme is crumbling.

Emails leaked at the weekend suggested senior civil servants regard the planned 2008 introduction of ID cards as unworkable.

And John Reid has ordered a review of the implementation of the flagship scheme.

A Home Office spokesman told the BBC: "We set a timetable for when ID cards would be introduced and that might change.

"That is dependent on the review that the home secretary is carrying out."

The implementation timetable was described as "very much secondary to the review the home secretary is carrying out".

Responding to the news shadow home secretary David Davis said: "This ID card project continues to crumble as doubts about its effectiveness, technology and cost pile up.

"It is becoming ever clearer, even from the government's own perspective, that they should abandon this expensive plastic poll tax which, far from improving our security, may well make it worse."