MPs who rushed back early from their holidays for a historic Commons vote on military action in Syria will instead be engaging in a little more than a grand parliamentary gesture after David Cameron was forced into a last-minute compromise by Labour.

The prime minister started the day with ambitions to put military action against Syria into motion with a decisive vote in the Commons. But he ended it with little more than a “dog’s motion” after Ed Miliband threatened to vote down his plans.

“It’s not so much a dog’s breakfast as a dog’s motion,” tweeted Sarah Wollaston, a Tory backbencher. “What’s the point of a recall for an expensive, whipped and now meaningless vote?”

Mr Cameron had not planned it so, but he was left with little option but to back down on the vote after Labour indicated that it would not support the government if it did not cross a series of additional hurdles. “The point is the PM wants to be consensual,” said one No 10 insider last night. “He wants to bring parliament and the public with him.” But in reality, he was facing an embarrassing defeat.

The Labour leader had previously signalled that he broadly supported of plans to back the US in a missile strike on Syria after several conversations with the prime minister this week.

But his position shifted after Ban Ki-moon, UN secretary-general, said inspectors in Syria needed more time to gather evidence of the alleged chemical attack in eastern Damascus.

The Labour leader at 6pm called on Mr Cameron to return to parliament a second time with proof not only that chemical weapons were used but also that the Assad regime was responsible.

A spokesman for Mr Miliband said the party had decided not to give a “blank cheque” to the coalition. “We’ve been here before when we didn’t wait for weapons inspectors.”

In theory Mr Cameron could have just about scraped a vote in the Commons with heavy whipping of Tory and Lib Dem MPs.

The prime minister has been holding private meetings with some recalcitrant MPs to try to build support. A senior Conservative said last night that Downing Street would be publishing a summary of evidence from the joint intelligence committee in an attempt to win over sceptical MPs on both sides.

In practice, however, dozens of coalition MPs were likely to rebel against the government – prompting Mr Cameron’s surprise volte-face at 7pm.

Thursday’s marathon eight-hour debate will now see MPs invited to deplore the use of chemical weapons and back the worldwide prohibition on the use of such weapons.

The motion also calls for a strong humanitarian response which “may, if necessary, require military action that is legal, proportionate and focused on savings lives”.

Downing Street will deplore the failure of the UN Security Council to respond adequately and note the international support for a response.

However the motion will suggest that the world should follow a “UN process” as far as possible and wait for the investigators in Damascus to complete their “initial mission”.

Every attempt will be made to get a Security Council resolution in favour of military action and the motion has also been worded “to alleviate humanitarian suffering” and does not sanction any military action with wider objectives.

Most importantly there will now be a second vote in the Commons, as demanded by Labour.

Mr Miliband had shifted his position as numerous Labour MPs warned their leader about their reluctance to back the action – with junior shadow health minister Diane Abbott threatening to resign.

MPs of all parties are wary about the potential for exacerbating an already horrendous situation in Syria. As such Mr Cameron may have a relatively easy ride on Thursday but will face sustained hostility if he returns for a second vote with such grave implications.

Tory MPs including David Davis, Douglas Carswell and John Baron had all said they would vote against the government if it failed to make a compelling case for the military strikes.

Public opinion in Britain is largely sceptical of intervention, with a YouGov poll showing 50 per cent opposed and 25 per cent in favour.

For many Labour MPs the situation has visceral echoes of 2003, when more than 100 of their ranks stood up to Tony Blair, then prime minister.

Graham Allen, a Labour veteran, said: “There are a sizeable group of people who do not want to commit to an open-ended adventure into the multinational incredibly complex situation in Syria.”

Get alerts on Syrian crisis when a new story is published

Copyright The Financial Times Limited 2018. All rights reserved.

Follow the topics in this article