A vote for the Conservatives is a vote to escalate the war in Syria and prolong the suffering of its people, Labour has said, after it emerged that Theresa May could try to push a motion through the House of Commons on joining military action against Bashar al-Assad if she wins next month’s election.

Emily Thornberry, the shadow foreign secretary, said such a move would “risk open conflict between our armed forces and those of Russia and Iran” and could lead the UK to repeat the mistakes of the Iraq war. She warned May against allowing the UK to “follow Donald Trump’s lead with blind loyalty, no matter where it takes us, and no matter what our other allies think”.

Labour, the Liberal Democrats, the Scottish National party and Greens are lining up to oppose any escalation of military action against the Syrian president, but May would find it easier to defy them and Tory backbench rebels if the polls are correct that she is on course for a sizeable majority on 8 June.

Thornberry raised the stakes with a warning that backing the Tories was a “vote to repeat the mistakes of Iraq from a prime minister who just last weekend refused to accept that she got Iraq wrong”.

She added: “Instead of this headlong rush to war, the British government should be working flat out through the United Nations to support the current talks on de-escalation of the conflict, with a view to creating a permanent ceasefire, a political solution and a lasting peace. That is what the Syrian people need, not Theresa May’s secret plans to escalate the war.

“These reports also reveal that – even on matters of peace and war – Tory MPs cannot be trusted to think independently and do what is best for the country. This increasingly authoritarian prime minister just sees them as voting fodder and, if they are prepared to back her rush to war, they will also surely vote for a chaotic Brexit and the dismantling of our NHS. The only way to stop them is to vote Labour.”

The Liberal Democrat leader, Tim Farron, said it was deeply worrying that May “would back military intervention against Assad in Syria outside of a wider diplomatic strategy and without UN backing”. He said Donald Trump’s bombing of Syrian regime assets last month was a proportionate response, and the use of chemical weapons was indefensible, but it was wrong to have gone ahead “unilaterally, without allies, outside of a wider strategy”.

Farron went on: “May would be wise not to use Syria as a campaign tool in this election. This would come across as calculating, unconsidered, and without the best interest of the Syrian people at heart.”

Downing Street has not confirmed whether it wants to hold a vote on military action, but a Whitehall source indicated overnight that May wanted Commons backing in order to have the freedom to join the US in airstrikes against the forces of Assad in the event of another chemical attack on the rebels.

The Labour leader, Jeremy Corbyn, a longstanding anti-war campaigner, warned May last month against unilateral military action in Syria. “We don’t need unilateral action. We need to work through the UN, but, above all, we need to bend ourselves totally to getting a political settlement in Syria,” he said.

Conservative opponents of military action in Syria were reluctant to speak against the plan on the day of the local elections and in the middle of a general election campaign. But two Tories who are expected to be re-elected as MPs told the Guardian their opposition to strikes on the regime in 2013 still stood.



David Davis, now the Brexit secretary, Julian Lewis, the chair of the Commons defence committee, and Crispin Blunt, the chair of the Commons foreign affairs committee, were among the 30 Conservative MPs to rebel against David Cameron’s motion at the time.Other former rebels, including Andrew Tyrie, Sir Richard Shepherd, Sir Peter Tapsell and Andrew Turner, will no longer be in the Commons if a post-election vote is held.

The UK is keen to line up fully alongside the US. It is already engaged with them in military action in Syria and Iraq against Islamic State, but has not joined in the airstrikes against Assad’s forces.



Russia, which is backing Assad, is said to be seeking new “safe zones” in Syria after talks with the US and Turkey.



Caroline Lucas, the joint leader of the Greens, called on May to come clean about her ambitions. “If Theresa May is planning further military action in Syria, then she should come clean with voters and lay out her plan,” she said. “People deserve a say on foreign policy and any attempt to wait until after the election to signal intentions in Syria is simply wrong.

“Parliament is united in horror at the carnage in Syria and the electorate deserve a chance to scrutinise how MPs from all sides will act on the issue if elected.”