Military action in Syria is expected over the weekend, with the PM likely to face down MPs

Theresa May has made a strident argument to her cabinet ministers that Britain should not allow the creeping erosion of the taboo of using chemical weapons that been an international norm since the first world war, the Guardian understands.

Downing Street said there is still no precise timetable for further military action, most likely to commence over the weekend, but the prime minister is understood to have argued in her opening address to cabinet that any British action in Syria should be limited to precise targeting of chemical weapons facilities and distribution.

May told her cabinet, which was recalled on Thursday to discuss next steps in the international response to the Douma chemical attack, that the UK’s intention was not regime change or prolonged involvement in the Syrian civil war.

US says it has proof Syria carried out Douma gas attack Read more

The prime minister has previously said her administration considers it highly likely Syrian forces were behind the atrocity. Speaking to ministers, she said the UK had long striven to uphold the international norm that the use of chemical weapons was abhorrent, but in recent years that norm had been eroded, citing a pattern of behaviour from the Assad regime in Syria. That norm must be restored, she said.

A government source said the prevention of the normalisation of chemical weapons was the whole rationale behind May’s decision that Britain should join any international response. Any agreed military response would be focused on that, the source said.

May spoke to the French president, Emmanuel Macron, late on Friday night, after speaking to Donald Trump overnight on Thursday.

Earlier on Friday, Jeremy Corbyn also accused May’s government of “waiting for instructions” from the US on how to proceed in the Syrian crisis, but said Trump was giving “alarmingly contradictory signals”.

The Labour leader and his Liberal Democrat counterpart, Vince Cable, received a security briefing from the government on Friday afternoon. Corbyn has insisted he wanted to see the evidence of who was behind the apparent chemical weapons attack in the town outside Damascus, which has killed more than 40 people.

“I want to know who did it. If there is proof the regime did it, they must be held responsible. If there’s a proof anybody else did it, they must be held responsible,” he said in an interview with Sky News.

“I would say very strongly to Russia and the US: ‘Stop blocking each other’s resolutions’.” Russia has repeatedly used its security council veto to block resolutions on Syria, including one on Tuesday that would have established an independent investigation into the suspected use of chemical weapons.

Corbyn denied that it was pointless, given Russia’s record, to continue to call for UN investigations. “Anything that brings a cessation of the use of chemical weapons moves us nearer, if not totally, to a ceasefire and a reopening of the Geneva talks which has got to be the right way forward.”

The prime minister is likely to face severe criticism from opposition MPs and members of her own party if she does not give MPs a vote in parliament on extending UK military action in Syria, but appears to be prepared to face down any condemnation if allies decide to act over the weekend.

Syria chemical attack: UN weapons inspectors to investigate site Read more

Any further delay would put intense pressure on May to hold a vote in parliament, which returns from recess on Monday. If the government does not offer a debate, both Labour and the Scottish National party are planning to demand that the Speaker, John Bercow, grants one on Tuesday.

Though Downing Street says no decision has been taken about the sequence of events, it will be argued that under royal prerogative May is not required to seek the permission of MPs, and under the convention that emerged after the Iraq war, she may also act alone in some circumstances, including to preserve the operational security but also to prevent humanitarian catastrophe.

The former attorney general Dominic Grieve has said there was no legal basis for a punitive raid to deter the Syrian regime from repeating what he called its “flagrant breach” of the international convention banning chemical weapons – except under the doctrine of humanitarian necessity. That is the UN convention on the responsibility to protect, agreed in 2005, which was the basis of David Cameron’s unsuccessful appeal to parliament over Syrian intervention in 2013.

A team of inspectors from the international chemical weapons watchdog is due to start an investigation on Saturday into the attack in Douma.