Speaking in Number 10, the Prime Minister warned Russia that the air strikes should act as a warning over its use of chemical weapons, following reports of the latest in a series of alleged gas attacks last weekend in the town of Douma which left more than 40 people dead.
Mrs May said the Cabinet had taken advice from the Attorney General, National Security Adviser and military chiefs when it met on Thursday before deciding on a joint response with Western allies, the United States and France.
“We agreed that it was both right and legal to take military action together with our closest allies,” she said.
Mrs May explained that four Royal Air Force Tornado GR4s joined the co-ordinated missile strikes at 2am on Saturday, launching Storm Shadow missiles at a base 15 miles west of Homs.
The Prime Minister went on to say that she had spoken to world leaders, including key regional figures such as Saudi Crown Prince Mohammad Bin Salman, King Abdullah of Jordan, and President Recep Tayyip Erdogan of Turkey, to explain why she had ordered British military involvement in the US-led strikes.
Nonetheless, Mrs May can expect to come under fierce questioning in the House of Commons tomorrow over her decision to order military action without putting the strategy to MPs first.
The Labour Party has called for a new act of parliament to prevent governments pressing ahead with military action without the backing of MPs in most circumstances, while Scotland’s First Minister Nicola Sturgeon has demanded that there is a full Commons debate.
She said that she too wanted a commitment from Mrs May that any further military action in Syria is authorised by a parliamentary vote.
“As well as not necessarily taking Syria a single step closer to peace, there is a real danger, and this is an extremely serious point, that air strikes such as those we saw over the weekend risk further escalating an already dangerous situation,” Ms Sturgeon said.
“The conflict in Syria is a complicated civil war but we see stand-offs between a range of other countries, proxy conflicts, being waged in Syria as well.
“So there is a danger that action that is taken hastily, action that doesn’t necessarily contribute to peace, actually risks not just escalating the civil war but escalating the tensions internationally as well.”
The Stop the War Coalition was planning to stage a protest against British military action in Syria outside Parliament tomorrow. A Leeds-based faction of the campaign group’s supporters are also set to stage a similar “emergency protest” in Leeds’ Dortmund Square at 5pm as an act of solidarity with their cohorts in the capital.
Campaigners have been further incensed by the choice of language deployed by US president Donald Trump on social media.
President Trump tweeted on Saturday after US, French and British planes and ships launched more than 100 missiles nearly unopposed by Syrian air defences and declared it was “mission accomplished”.
The strike was “perfectly carried out”, he said, and that “the only way the Fake News Media could demean was by my use of the term ‘Mission Accomplished’.”
He added that he knew the media would “seize” on the phrase, but he said that it should be used often.
The US president said that “it is such a great military term, it should be brought back”.
While he declared that the strikes had been a success, the Pentagon said that the bombing of three chemical-related facilities still left enough others intact to enable the Assad government to use banned weapons against civilians if it chooses.
Mr Trump’s choice of words echoed a similar claim associated with President George W Bush following the US-led invasion of Iraq.
President Bush addressed sailors on board a Navy ship in May 2003 alongside a “Mission Accomplished” banner, just weeks before it became apparent that Iraqis had organised an insurgency that tied down US forces for years.
The nighttime Syria assault was carefully limited to minimise civilian casualties and avoid direct conflict with Syria’s key ally, Russia, but confusion arose over the extent to which Washington had warned Moscow about the offensive in advance of the missile strikes.
The Pentagon said it gave no explicit warning.
However, the US ambassador in Moscow, John Huntsman, said in a video, “Before we took action, the United States communicated with” Russia to “reduce the danger of any Russian or civilian casualties”.