Sir Keir Starmer and Emmanuel Macron are cutting Donald Trump out of plans to patrol the Strait of Hormuz once the war against Iran is over.
The two leaders are piecing together a coalition of mostly European countries in a similar alliance to the French and British-led “coalition of the willing” nations working on Ukraine.
The idea is to send mine-sweeping and other vessels to clear the shipping lane and give companies the confidence to use the strait once the fighting is finished.
But the plan risks angering the mercurial Mr Trump, who has repeatedly castigated his Nato allies for failing to join his war and threatened to reconsider membership of the alliance.
European leaders have insisted this is not their war and ignored US calls to send warships to the strait.
They have rejected Mr Trump’s more recent demands for help in blockading Iranian ports to force Tehran to open the vital waterway, which carries about a fifth of the world’s oil.
The Prime Minister and the French president will host a video conference on Friday of several dozen countries to discuss how best to police the region after a permanent ceasefire.
Mr Macron said on Tuesday it would be an international defensive mission, which would not include the “belligerent” nations of Israel, Iran and the US.
“The mission we are referring to could only be deployed once calm has been restored and hostilities have ceased,” Jean-Noël Barrot, the French foreign minister, said.
He added that the coalition would coordinate with countries on the strait, including Iran, which could mean the mission would only go ahead with Tehran’s blessing.
Insiders told The Telegraph that the scale of the mission would be reminiscent of the operation during the Tanker Wars of the 1980s, which saw dozens of coalition vessels, including a carrier strike group, deployed to the region.
The Royal Navy has been readying the RFA Lyme Bay to operate as a potential command and control hub as part of the mission. Mine-hunting vessels, submersible, surface and aerial drones and warships for air defence would be deployed to the Middle East.
The plan aims to put logistics in place so that the hundreds of ships stuck in the strait could leave.
The next step would be a major demining operation so that a far larger number of ships could use the strait after Iran mined it in the early part of the war.
Europe has more demining assets – about 150 vessels – than the US, which has largely decommissioned its minesweepers.
Britain favours using drones to clear mines to keep vessels and therefore sailors as far away from danger as possible.
The mission would involve regular military escorts and surveillance by frigates and destroyers to give shipping and insurance companies confidence to use the Strait. How big that naval presence needs to be is unclear at this stage.
Air defence assets earmarked for the mission would be sent on a strict set of rules of engagement, only allowing for strikes against any incoming projectiles, as was the case with the European deployment to the Red Sea to defend cargo ships against Iran-backed Houthi rebels.
Some issues remain to be ironed out between the allies.
British officials reportedly fear not including the US would infuriate Mr Trump and ultimately limit the operation. French diplomats think involving the US would make the operation unacceptable to Iran.
Germany is expected to take part in the new mission, but any overseas military venture is politically difficult for Berlin because of its past in the Second World War. However, it does have the money and equipment needed for the mission.
The Italian government has said it will not send ships to the Strait after the war without a United Nations mandate.
Not under US command
Mr Macron has insisted that Europe must act more independently of Washington ever since Mr Trump’s first term and Friday’s discussions will be held amid mounting European frustration with the President.
Since returning to the White House, he has hit Europe with tariffs, threatened to invade Greenland, sidelined Europe in peace talks on Ukraine, undermined Nato and has now exacerbated a cost-of-living crisis by illegally attacking Iran without informing allies first.
The Wall St Journal cited European diplomats who insisted the ships would not be under US command. Officials told the newspaper that the US would not attend the online meeting.
China and India were invited, but it is not clear whether they will attend, a French official said.
