Westminster speculation has raised a new question mark over the future of the government's flagship identity card scheme, following news of the forthcoming departure of home secretary Jacqui Smith.

Smith was one of the main driving forces behind the ID card policy, fighting off Treasury concerns about cost and rejecting a Treasury-led proposal for a private-sector-led ID system.

But she has been badly tarnished by the row over her husband's claim for renting a porn video on her expenses and her designation of her main home as a room in her sister's London house. She is expected to leave the Cabinet in Gordon Brown’s expected reshuffle next week.

One of Smith’s possible successors, Alistair Darling, whom the prime minister failed to support as his ongoing Chancellor, is not known as a strong supporter of the ID scheme .

With budgets under pressure and if he gets the post, Darling may see the switch at the top as the opportunity to change the policy.

But there was late speculation that he might refuse the job and with the government itself in disarray following a co-ordinated series of resignations, the future of ID card policy is the last of Brown's problems.