Robin Cook has refused to deny suggestions that he will resign from the cabinet if MPs vote for an entirely appointed House of Lords.

Cook, the leader of the House of Commons, pointedly refused to dismiss suggestions that he may quit if MPs reject proposals for an elected element to the second chamber.

Speaking over the weekend, Cook warned that splits on Lords reform could result in there being no change to the composition of the upper house.

"I would advise colleagues to show some flexibility so that we can find common ground. What I don't want to see happen is that we end up with no reform because those that want reform can't agree with what sort of reform they seek," he told GMTV.

It has emerged that two of Labour's rising stars, David Miliband and Douglas Alexander, are set to defy the prime minister and back a largely-elected second chamber.