LONDON — Theresa May kept the U.K. in lockstep with the U.S. and France Thursday, on a steady march to military intervention in Syria.

As U.S. President Donald Trump prepared to be briefed on options for missile strikes in response to a suspected chemical attack in the town of Douma, and French President Emmanuel Macron said he had "proof" the Syrian government was behind the attack, the British prime minister gathered her Cabinet around her and agreed on a course of action that kept her in line with — but not ahead of — her two allies.

The response is typical of a prime minister renowned for her methodical, cautious approach to crises who has been forced to build consensus among a divided party while leading a minority government.

The Cabinet, including Brexit Secretary David Davis, who has in the past rebelled against his party to oppose military action in Syria, agreed it was "highly likely" Bashar al-Assad's regime was responsible for Saturday's attack, citing its "track record of the use of chemical weapons," a Downing Street spokesperson said, though the statement gave no detail on what the U.K. government planned to do about it.

The language echoed the U.K.'s case against Assad's ally Russia, when May accused Moscow of carrying out a nerve agent attack on a former spy in the English cathedral city of Salisbury last month. That incident prompted a united diplomatic response from the West in support of the U.K., with the U.S. leading the charge by expelling 60 diplomats.

It also marked a boost for May, long dogged by rumors of imminent political demise, whose fortunes also improved thanks to the agreement of a Brexit transition deal in Brussels and criticism of opposition leader Jeremy Corbyn's failure to decisively blame Russia for the Salisbury attack.

Now it is the U.K.'s turn to back its allies — despite the risks of a confrontation with Vladimir Putin's forces in Syria.

Cabinet position

In a discussion in which, Downing Street said, every Cabinet minister made a contribution, May secured agreement that it was "vital that the use of chemical weapons did not go unchallenged."

"Cabinet agreed on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime [and that] the prime minister should continue to work with allies in the United States and France to coordinate an international response," the spokesperson said.

However, officials would not be drawn on whether ministers discussed another critical element in May’s calculation — the role of the U.K. parliament in committing British forces to action. If the U.S., France, the U.K. launch strikes before Monday when the House of Commons returns from its Easter recess, MPs will get no say in the decision unless May takes the rare step of recalling parliament.

The prime minister faces pressure from all sides to seek the backing of parliament, with calls from her own MPs and opposition parties for a rare Saturday sitting of the Commons to authorize any action.

Labour Party leader Corbyn, SNP Westminster leader Ian Blackford, and Liberal Democrat leader Vince Cable have all called for a vote, as have several senior Conservative MPs.

From a strictly legal point of view, May does not need one — decisions on military action are covered by her royal prerogative powers as prime minister. However, there are several precedents, since the vote on the U.K.’s involvement in the 2003 Iraq War, for MPs being consulted and in 2013, the House of Commons voted against military action against the Assad regime.

"When our country comes under attack, the government may have to act first and seek parliament's approval afterwards,” said Julian Lewis, chair of the House of Commons defense committee. “But when we are contemplating military intervention in other people's conflicts, parliament ought to be consulted first.”

Ken Clarke, a former chancellor of the exchequer and the House of Commons’ longest-serving MP, agreed.

“In a modern parliamentary democracy, you’ve got to have parliamentary approval if you have a planned policy decision to launch a military attack of any significant size,” he told BBC Radio 4. “All this stuff about invoking the royal prerogative so that on treaties or going to war the Cabinet is a kind of autocracy is, I think, extremely dangerous.”

Clarke added that MPs should be recalled early from their Easter break, over the weekend if necessary. Such Saturday sittings are very rare, with only four occurring since 1939, marking events including the outbreak of World War II and the Falklands War.

However, other senior Tories offered May cover to press on without a vote. The chair of the House of Commons foreign affairs committee, Tom Tugendhat, said the law favored May’s preference not to consult MPs. “If she did ask for a vote I think she would win it but I don’t think she needs to ask for it,” he told BBC Radio 4.

Iain Duncan Smith, a former Conservative leader, said if a military strike had to be made quickly, the government should “get on with it” adding that a House of Commons vote could happen after the event, as occurred with the U.K. intervention in Libya in 2011, a vote that passed with only 13 MPs voting against.

Labour split

Three of those 13 opponents on the Libya vote are now senior members of the Labour’s shadow Cabinet — Corbyn himself, Shadow Chancellor John McDonnell and Shadow Trade Secretary Barry Gardiner — and seem likely to oppose air strikes.

But any vote — either before or after action — could present problems for the party, which suffered a rancorous split the last time MPs voted on military action, against ISIS in Syria in 2015. Corbyn has a long record of opposing Western military interventions and on Thursday made clear his view that “more bombing, more killing, more war, will not save life” in the current instance of mooted action against Assad.

According to one senior party figure, the Labour leader on Thursday asked the government for a security briefing on Syria on privy council terms — involving an oath of secrecy that allows Corbyn as leader of the official opposition to see restricted information on matters of national security.

It is probable that, despite their leaders’ opposition, a number of Labour MPs — many of whom openly oppose Corbyn — may back military action. In 2015, Corbyn granted a free vote on air strikes on ISIS in Syria, rather than instructing his party how to vote. Labour officials said it was too early for any decision on what Corbyn would tell Labour MPs this time round for an as yet unannounced vote.