Theresa May avoided a vote in parliament on Syrian air strikes because she knew she would lose

Last year, Donald Trump launched strikes within three days of a chemical weapons atrocity, but this time he waited a week, giving Britain and France time to join him – but also giving May time to consult parliament if she wanted to

On the gravestone of Robin Cook, leader of the House of Commons at the time of the invasion of Iraq, is an inscription: “I may not have succeeded in halting the war, but I did secure the right of parliament to decide on war.”

It wasn’t true, as was confirmed last night. The evolution of the convention that the House of Commons should approve military action is more complicated than most people, including Cook, realised.

Legally, the decision to go to war is taken by the Queen acting through and on the advice of her ministers. It is a decision of her government, which derives its authority from its command of a majority of MPs in the Commons, but it does not require a vote of MPs beforehand.

Clement Attlee did not ask the House to vote to join the US in the Korean war in 1950, although Winston Churchill, who supported it as leader of the opposition, argued that the prime minister should have done. “It is better to have a division so that everyone can know how the House of Commons stands and in what proportion,” Churchill said, despite the danger that a “handful of dissenters” might create “false impressions” abroad that the country was disunited.

Anthony Eden did not put Suez to a vote. Margaret Thatcher didn’t ask for a vote before dispatching the task force to retake the Falklands, although parliament was recalled on a Saturday when the Labour opposition led by Michael Foot urged her on. John Major did not have a vote on the Gulf War in 1991, although 57 MPs, including Jeremy Corbyn, recorded their opposition by the procedural device of voting against a motion to adjourn.

Then came Tony Blair and Robin Cook. Cook was foreign secretary when Saddam Hussein defied the UN by expelling its inspectors from Iraq in February 1998. For the first time, the prime minister agreed to put the question of the use of force to an explicit vote of MPs on a government motion. It was carried by 493 votes to 25, and Saddam backed down, but Blair regretted giving the 25, again including Corbyn, the chance to express their opposition. He would not do so again until 2003.

When Saddam again ended cooperation with UN inspectors at the end of 1998, Blair refused to give the Commons a new vote, and resorted to a procedural ambush to prevent Corbyn and others voting on a motion of their own. British jets joined the US air force in a four-day bombing campaign called Operation Desert Fox.

Blair denied MPs a vote on action in Sierra Leone and Kosovo. Corbyn was again among the handful of Labour MPs who engineered a protest vote after the bombing of Serbia had started in 1999 – at the time enraging Clare Short, international development secretary, who called them “a disgrace to the Labour Party” and, in an interview the next day, “like those who appeased Hitler”.

It wasn’t until the Iraq war of 2003 that MPs were again to vote on a government motion explicitly to approve military action. This was the basis of Cook’s posthumous claim: but the vote was a product of its time. Partly because that invasion was so long in preparation, contrary to the cliché of the “rush to war”, it became impossible for Blair to avoid a vote. His cabinet and party would not have allowed it: as it was, half of his backbenchers voted against the government.

Nearly a decade later, David Cameron held a vote on Libyan air strikes in 2011 – but after the event, rather than before, on the grounds that it was urgent action to avert a massacre. Then, in 2013, he lost a vote to authorise strikes in Syria that would have been similar to last night’s: designed to deter Assad’s use of chemical weapons. That vote had consequences, in tipping Barack Obama away from launching US strikes himself.

On that occasion, Ed Miliband changed his position late in the day after opinion polls suggested strikes were unpopular. But the decisive group were the 30 Conservative MPs who voted against Cameron – a group that Theresa May knows are still there, even if some of the faces are different after two elections.

She knew, too, that Labour interventionists (many of whom bitterly regret obeying the party whip in 2013) and the DUP (who voted against in 2013 but support her today) were not enough to guarantee that she would win a vote this time.

That is why, although she could have recalled parliament on Thursday, when the cabinet held an emergency meeting, she chose not to.

No wonder she was so inarticulate when asked this morning why she hadn’t gone to parliament. She said the response had to be “timely” and she was “working with international partners”. The first is unconvincing and the second, that the timetable – as Corbyn alleges – was set by President Trump, is worse.

Last year, Donald Trump launched strikes within three days of a chemical weapons atrocity, but this time he waited a week, giving Britain and France time to join him – but also giving May time to consult parliament if she wanted to.

She could have had a vote on the principle of punitive strikes designed to deter Assad from breaking the Chemical Weapons Convention again. Just as Blair held that vote in 1998 on the principle of strikes to force Saddam to comply with the UN. But she might have lost, whereas Blair won overwhelmingly.

She will have to explain, when she faces the House and the ghost of Robin Cook on Monday, why she chose to defy parliament and public opinion. In a democracy, there ought to be a price to pay.