And Macron also defended the move as one of his constitutional powers in a TV interview on Sunday.

“This mandate is given democratically to the president by the people in the presidential election,” said Macron, 40, who became France’s youngest president in May 2017. 

After May ordered the attack, Jeremy Corbyn, leader of the opposition Labour Party, called for new legislation to stop governments launching military action without lawmakers’ backing in most circumstances.

“The prime minister is accountable to this parliament, not to the whims of the US president,” he told a packed chamber.

May, who has been in office since July 2016, rejected the notion that she took orders from US President Donald Trump, saying her decision was based on Britain’s national interest.

But she avoided answering questions on whether parliament would be consulted on any further strikes and ignored Corbyn’s for the so-called War Powers Act. 

Macron clarifies Syria remarks after suggesting he persuaded Trump

Britain has said there are no plans for future strikes against Syria. Foreign minister Boris Johnson, in Luxembourg, again said the strikes were not aimed at regime change in the country, but rather designed to send a message.

Following Washington’s military lead remains a sensitive subject in Britain, where memories of participation in the US-led invasion of Iraq in 2003 are still raw.

May also said that “We have not done this because President Trump asked us to do so. We have done it because we believed it was the right thing to do.”

But a poll showed scant public support for the move.

The poll, by Survation for The Mail on Sunday, showed 36 per cent in favour of Britain’s participation in the air strikes, 40 per cent against and the remainder undecided.

Of the survey’s 2,060 respondents, 54 per cent also agreed with the statement that May “should have held a parliamentary debate and vote before intervening militarily in Syria”.

Ian Blackford, the leader of the opposition Scottish National Party in Westminster, was one of many who asked May why she had not recalled parliament for a vote, breaking with a convention dating back to the 2003 invasion of Iraq. 

“The prime minister leads a minority government,” he said. “It was perfectly possible for the house to have been recalled in advance, why was this not done?”

What we know about probe of Syria’s alleged chemical weapons use

May’s speech was followed by a heated debate during which some MPs called on Britain to welcome more Syrian refugees – rejected by May – and continue the diplomatic push to end the seven-year conflict.

Outside the Houses of Parliament, the Stop the War coalition – once led by Corbyn – was due to hold a demonstration.

The group said the strikes “will have done nothing to end the war” and “risked dramatically widening” the conflict.

In France, Macron has faced similar criticism from both the right and the left for attacking Syria without consulting the legislature.

National Front leader Marine Le Pen has accused Macron of failing to show any evidence on the use of chemical weapons by the Syrian regime to justify the strikes.

Jean-Luc Melenchon, head of the hard-left France Unbowed party, has also condemned the strikes, while the leader of the centre-right Republicans party, Laurent Wauquiez, said he “did not believe in punitive strikes”.

But at a press conference in Paris on Monday, Macron said France had acted with “international legitimacy”.

He argued that the operation was legitimate despite not being sanctioned by the UN since under a 2013 UN resolution Syria was supposed to destroy its chemical weapons arsenal.