Former Labour cabinet minister Peter Hain told the Guardian he felt intervening in Syria would be "very dangerous".
Mr Hain, who is poised to vote against the motion when Parliament meets tomorrow if he returns from a foreign trip in time, said: "The Prime Minister is asking the nation to back him on a dangerous strike when nobody knows what the consequences will be. I think that's very, very dangerous politics."
The Prime Minister has said 'the world should not stand idly by' after hundreds were killed in apparent chemical attacks in Syria last week.
Any UK military action in Syria would involve submarine-launched cruise missiles rather than air strikes, a military expert has predicted.