Oliver Letwin is said to be backing plans for pacifist taxpayers to be allowed not to contribute to the government's defence spending.

The shadow chancellor has been named as a supporter of "Conscience: The peace tax campaign".

This group wants the law to be changed to allow conscientious objectors to have their money spent on "peace building initiatives" instead of the military.

Letwin's spokesman said it was his personal belief rather than party policy.

Fraser Kemp, Labour's deputy election co-ordinator, said: "For Oliver Letwin to consider something that could threaten the defence of the realm is unbelievable.

"The fact that he could be won round to this cranky idea demonstrates that he shouldn't be trusted to be in charge of a whelk stall, let alone the national economy."