The Foreign Minister had suggested it would be hard to turn down a request to support Donald Trump if there were further Syrian chemical attacks.
Theresa May has dismissed as “hypothetical” a suggestion from Foreign Secretary Boris Johnson that it would be difficult to say No to supporting further US air strikes against Bashar Assad’s regime.
The Prime Minister stressed the importance of finding a solution with a “political transition away from president Assad”.
Mr Johnson had suggested it would be hard to turn down a request to support Donald Trump if he sought to launch further strikes in response to any use of chemical weapons by the Syrian regime.
And the Foreign Secretary indicated that the Prime Minister might not seek MPs’ approval in a parliamentary vote before British forces were deployed.
Mrs May sought to play down the prospect of military action, saying: “This is a hypothetical issue because there is no proposal on the table for further strikes in Syria.
“What is important is that we look to see how we can bring about a solution in Syria that is going to lead to a strong and stable Syria. That means a political transition, it means political transition away from president Assad.”
On a campaign visit in Chesterfield she said the UK had been at the forefront of diplomatic efforts to say to the Syrian regime’s backers, including Russia, that “now is the time to stop president Assad from bombing his own people”.
Liberal Democrat leader Tim Farron said it was “critical” for ministers to obtain Parliament’s consent before taking action, and warned Mrs May not to do so under cover of the election period, when there were no MPs in place.
Labour leader Jeremy Corbyn said the Government should focus on securing a political settlement in Syria, rather than taking unilateral action.
Mr Johnson said there was “no question” that Assad’s regime was responsible for the sarin gas attack earlier this month which prompted a US retaliatory cruise missile strike on a Syrian air base.
Asked whether Britain would be ready to join the US in similar action if the chemical assault was repeated, Mr Johnson told BBC Radio 4’s Today programme: “I think it would be very difficult for us to say no. How exactly we were able to implement that would be for the Government, for the Prime Minister.
“But if the Americans were once again to be forced by the actions of the Assad regime – don’t forget, it was Assad who unleashed murder upon his own citizens with weapons that were banned almost 100 years ago – if the Americans choose to act again and they ask us to help, as I say, I think it would be very difficult to say no.”
Britain is carrying out air strikes in Syria and Iraq against terrorists of the so-called Islamic State (IS), but has taken no military action against the Assad regime.
MPs backed the action against IS in a December 2015 Commons vote but rejected strikes against the Syrian government in 2013.
Mr Johnson said that the question of whether parliamentary approval would be needed for any military action “needs to be tested”.
Pressed on whether the Government would have to bypass Parliament if there was a phone call in the night calling on the UK to support US action, he told LBC radio: “You are putting your finger on the issue.”
There is no legal requirement on the Government to seek parliamentary approval before ordering military action but it has become convention to consult MPs, except in the event of an emergency.