Donald Trump has left his supposed allies in a dire position. His war on Iran failed to bring down the ayatollahs’ regime and has led to the worst global energy crisis in half a century.

Even if the conflict ends immediately – and with this President, anything is possible – the fallout will last for at least several more months. The world’s arteries have been blocked, and recovery from this economic heart attack will take time in any scenario.

Sir Keir Starmer’s position is clear: Britain is not involved in attacking Iran and will not become involved, beyond defensive moves to block reprisals from Tehran. Unusually, he has been consistent on this from the start of the war rather than twisting and turning as he so often does.

The Prime Minister is now looking to reap some political rewards. Both Reform UK and the Conservatives initially argued, after the first 48 hours of the conflict looked like a success, that British troops should have gone into action along with the Americans. They have both changed their tunes, and Starmer delights in pointing this out.

But he has been reluctant to go further and risk angering Trump. Starmer never says explicitly that he believes the war was a mistake from the get-go, only that it is not for the UK to get involved with. Most other Nato allies have taken a similar approach, taking sideswipes at the President’s decisions without actively opposing them.

Increasingly, there is little to lose from being more direct. The war looks to be immensely unpopular: a YouGov poll in early March suggested that 59 per cent of Britons are against it with 25 per cent supporting, a gap that has surely grown since then given the lack of tangible progress and growing economic impact. In the US too a solid majority of voters express opposition to the conflict.

Starmer has had some success with the “Trump whisperer” act he adopted for the first year of the current US administration, growing surprisingly close to the mercurial President. That has now gone out of the window, with front-page articles in The New York Times warning that the Prime Minister is now a “punchline and punching bag” for his erstwhile friend.

It is understandable that he does not want to face up to the failure of this strategy. It is not Starmer’s fault: Trump has made it impossible for his allies to stand by him with his posturing over Greenland and now this war so misguided that the President himself cannot explain why he is attacking.

But this is an opportunity – not only to do the right thing, but to shore up his own position at a time when there are still questions over the Labour leadership.

Time and again, Starmer has faced the claim that he does not know what he stands for and cannot communicate a consistent message to the public. He can start to dispel that by being brutally frank: this war is a mistake. It is making us poorer. And the world is getting no safer, notwithstanding the brutality of the Iranian regime and its track record of sponsoring terrorism abroad.

If done in co-ordination with the leaders of other countries such as France, Germany, Canada and Japan, this honesty could help bring the war towards a speedier end. Showing key Trump aides and other senior Republicans that the US stands alone, with only Israel in support, could help persuade them that they are on a hiding to nothing with this conflict.

There are risks, of course. The President is already threatening to reconsider American membership of Nato – although this is not something he could legally do without the backing of Congress or the Senate. When he is weakened, he has a tendency to lash out more even aggressively than normal.

But the time has come for Starmer to take a stand. He has an example to copy close at home – Rachel Reeves told the BBC on Wednesday: “I’m angry that Donald Trump has chosen to go to war in the Middle East – a war that there’s not a clear plan of how to get out of.”

That passion has long been lacking from 10 Downing Street. The Prime Minister finally has a chance to show the fire in his belly.

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