The UK prime minister will address parliament on Monday to defend and explain Britain's role in bombing Syria over suspected chemical weapons attacks.
Theresa May is under fire for bypassing the House of Commons. Some MPs are calling for a potentially damaging vote on her future strategy.
Speaking on the BBC's Andrew Marr show on Sunday, the opposition leader Jeremy Corbyn, has questioned the legality of the air strikes: As a member of the Security Council, as a country with a long tradition of international involvement, should we say, then we have to abide by international law. And I say to the foreign secretary, I say to the prime minister, where is the legal basis? The legal basis would have to be self defence or the authority of the U.N. Security Council."
"She could have recalled parliament last week ... or she could have delayed until tomorrow, when parliament returns," added the veteran peace campaigner.
The British government says it has no plans to repeat missile strikes on Syria, but it will consider further action if President Bashar al-Assad again uses chemical weapons against his own people.
"I hope that this will be a deterrent to him and obviously I hope that it will mean no further humanitarian suffering by the Syrian people as a result of the use of chemical weapons," said UK Foreign Secretary Boris Johnson.
"If he should be so cruel and so reckless as to do it again, now that is a separate point. That's a separate proposition and we would have to look, together with our colleagues, at what the options were then."
Opinion polls suggest most Britons do not support military action.
Carried out by Survation, one survey of just over 2,000 people taken after the strikes were launched, found that 40 percent were opposed. Some 36 percent were in favour of the military action.
Still scarred by Iraq, many in the UK fear getting embroiled in another costly conflict in the Middle East.