Labour leader Jeremy Corbyn has written to Prime Minister David Cameron asking for a two-day debate on air strikes in Syria.
In a letter sent this afternoon beginning "Dear David", Corbyn said the matter is "of such critical importance there must be full and adequate time for any debate".
"A one day debate would inevitably lead to important contributions being curtailed," Corbyn said, adding the debate would be "much better informed" if it included views from the foreign affairs and defence select committees.
Downing Street has repeatedly said that Cameron will not call a Commons vote on extending British anti-ISIS air strikes to Syria unless he is sure he has a clear majority of MPs supporting him.
With the Prime Minister in Paris today for climate change talks and expected to be out of the country on Thursday and in his constituency on Friday, most have expected the vote would come on Wednesday.
Corbyn, who opposes extending the strikes, was scheduled to meet with members of his shadow cabinet to discuss the issue at 2PM today.
Earlier in the day, Corbyn's office released a poll showing 75 per cent of Labour members are against the plan.
The poll was based on 107,875 responses to an email sent out by Corbyn last Friday. The Labour party said it found just 13 per cent in favour of UK bombing in Syria, 11 per cent undecided and 75 per cent against.
The news comes after shadow chancellor John McDonnell said Labour MPs should be given a free vote, but close ally Diane Abbott said MPs must follow the leadership.
She told BBC Radio 4's Today programme this morning: ""I think it's clear now that Cameron's case [for war] is unravelling. Party members and increasingly the country want to see us oppose these air strikes."
Corbyn could face a revolt if he forces shadow cabinet members and Labour MPs to support him, while former Labour leader and Prime Minister Tony Blair has also said that Cameron can rely on the support of "many Labour MPs".