Image copyright AFP Image caption The UK says it has "little doubt" the Syrian regime was behind April's deadly attack

MPs could be asked to approve military action in principle in Syria in case of further chemical weapons attacks, two senior Conservatives have argued.

Crispin Blunt and Johnny Mercer said Parliament's approval should be sought in advance for the subsequent use of force should there be more atrocities.

Hard intelligence, legal clarity and limits on action were needed, they say.

Parliament rejected the case for action against the Syrian regime in 2013 after a suspected chemical weapons attack.

And Downing Street said there were "no plans" for Parliament to revisit the issue.

Pressure has been growing for action in the wake of an attack on Khan Sheikhoun, a town in Northern Syria held by rebel forces fighting the government, on 4 April which killed 90 people.

The Organisation for the Prohibition of Chemical Weapons (OPCW) found the attack could only be "determined as the use of sarin, as a chemical weapon".

Although the UN has yet to officially determine who was responsible, and the Syrian authorities have denied any involvement, the UK says it believes the government of Bashar al-Assad was responsible.

US President Donald Trump launched a limited bombing campaign against regime military targets in Syria in response.

Speaking in late April, Foreign Secretary Boris Johnson suggested that if the US asked the UK to join them in military action in the event of further chemical weapons attacks, it would be "very difficult" to say no.

He also said the recent convention that Parliament has to give prior authorisation to the use of force would need to be "tested".

Image caption The coalition government lost a vote on military intervention in Syria in 2013

Parliament rejected action against the Assad regime in 2013 as Labour voted against and nearly 40 Tories and Lib Dems rebelled. MPs later sanctioned the bombing of so-called Islamic State positions in Syria.

Mr Blunt - a former chairman of the Commons foreign affairs committee and Mr Mercer - a former member of the defence select committee - are now calling for a different approach in which the government should consider getting parliamentary authorisation on a pre-emptive basis if certain conditions are met.

In a new briefing paper published in association with the European Council of Foreign Relations, the two MPs argue the government failed to get the support of Parliament in 2013 because it "rushed" the vote, did not give sufficient guarantees over the legality of the proposed action nor provide timely intelligence.

'Unprecedented'

While a pre-emptive vote would be "unprecedented", they argue that action may be needed given that chemical agents continue to be used despite the Syrian regime signing up to the Chemical Weapons Convention in 2014 and, in an initiative sponsored by the Russians, removing all declared chemical weapons.

Such an approach, they say, would give the government sufficient time to make a "clear and thorough" case for action, set out the threshold for the use of force, spell out what limitations would be placed on any intervention and how it would relate to wider attempts to end the six-year civil war in Syria.

"It would probably be impossible to get parliamentary authority for UK reprisal action within the likely timeframe of a US military response to a chemical weapons attack in Syria," Mr Blunt - who was among those to vote against military action in 2013 - said.

He added: "Pre-emptive parliamentary authority would send a deterrent message in itself, help address the complex legal and strategic questions involved, as well as enable limitations on military action to prevent escalation and mission creep."

Mr Mercer, a former soldier who was first elected to Parliament in 2015, said the paper set out some new ideas about how the UK might respond to atrocities of the like seen in Syria since 2013 given the "bruising" legacy of its experience in Iraq.

"I hope that this paper gives genuine food for thought as to how we as a country can back up what we say with what we do and highlight a clearer path as to when we may or may not intervene," he added.

Without an absolute majority in the Commons, the government would find it difficult to win any vote on military action without the support of a large number of Labour MPs, whose leader Jeremy Corbyn is a vehement critic of foreign intervention in the Middle East.

The SNP has warned ministers against by-passing Parliament and "falling blindly in line to the Trump tune".