Labour MP Nick Brown has called on party members to demand a full debate on the future of Britain's Trident nuclear weapons system at next year's party conference.
The former chief whip told a Labour CND meeting at the House of Commons on Tuesday night that he was against Trident in 1983 and he was against it now.
Mr Brown told the meeting that the Tories were confident with Trident renewal and Labour activists needed to push the arguments against it.
"The decision will be made in the next Parliament and we need an answer," he said.
"Being credible on defence is not the same as supporting Trident renewal. It sends a bad message to the world."
Mr Brown added that it was crucial that members press for a debate at next year's conference.
Foreign Minister Alistair Burt's admission that the Cameron government has "supported" a survey of attitudes to US drone strikes in Pakistan's tribal areas amounts to a tacit admission of British involvement.