Keir Starmer could have to give the green light for US bombers to use the Diego Garcia military base for strikes on Iran.
Donald Trump is keeping the world guessing about whether he will join Israeli attacks on Tehran’s nuclear facilities.
The PM has been urging ‘de-escalation’ and so far UK forces are not thought to have played a direct part in defending Israel from retaliation.
However, Sir Keir might be forced to choose amid speculation that B-2 stealth bombers would use the Chagos Islands airbase if they are brought in to target an enrichment plant deep under a mountain.
There are concerns that would leave UK assets and personnel facing reprisals, with RAF Akrotiri on Cyprus a potential target. More jets have been moved into the region to bolster security.
With the situation on a knife edge, David Lammy will hold talks with the US secretary of state Marco Rubio in Washington later.
After seeing Mr Trump at a G7 summit in Canada earlier this week, Sir Keir insisted that he did not think the US was on the verge of joining the operations against Iran.
But the premier convened an emergency Cobra meeting yesterday to take stock of diplomatic efforts and UK support for British nationals in the region.
There are claims that Attorney General Lord Hermer has been advising that the UK can only legally take part in military actions to defend allies.
Mr Trump told reporters outside the White House he was considering strikes on Iran’s nuclear facilities.
He said: ‘I may do it. I may not do it. I mean, nobody knows what I’m going to do.’
Israel and Iran have been exchanging fire for days after Benjamin Netanyahu announced a campaign to prevent Tehran from developing a nuclear weapon.
Iranian officials insist the country’s nuclear programme is peaceful, and claim Israel has caused hundreds of civilian casualties. A previous deal to limit Iran’s enrichment of uranium was torn up by Mr Trump during his first presidency because he regarded it as too weak.
The Israeli military has urged residents to evacuate the area around the Arak heavy water reactor, about 155 miles south west of the capital.
Iranian state television said the reactor had been attacked, but had been evacuated and there was ‘no radiation danger whatsoever’.
The Soroka Medical Centre in Beer Sheba, the main hospital in southern Israel, received ‘extensive damage’ after being hit by an Iranian missile, according to a spokesperson for the hospital.
Iran’s Supreme Leader Ayatollah Ali Khamenei has rejected Mr Trump’s call for surrender and warned American military involvement would result in ‘irreparable damage’.
Nuclear talks with Iran and senior diplomats from the UK, Germany and France as well as the EU will take place in Geneva tomorrow.
In his comments outside the White House, Mr Trump had suggested the US could still hold talks with Iran.
‘I can tell you this, Iran has got a lot of trouble and they want to negotiate,’ he said.
He said ‘it’s very late to be talking’, but ‘we may meet’.
Under the recently agreed deal to hand back the Chagos Islands, the UK leases the DIego Garcia base from Mauritius, while the US pays for its operating costs.
Sir Keir had played down the prospect of US intervention, telling reporters at the G7 that ‘nothing’ he had heard from the president suggested Washington was poised to get involved.
Asked yesterday whether the Prime Minister was confident that Mr Trump would not involve US forces in the conflict, a No10 spokesman said the UK’s position was still that ‘we want to de-escalate rather than escalate’.
The US State Department has started evacuating non-essential diplomats and their families from the American embassy in Israel.
The US is also making plans for evacuation flights and ships for private citizens, the country’s ambassador to Israel said.
The UK’s Foreign Office has evacuated family members of embassy staff from Israel, but has not advised British nationals to leave the country.
The department said the evacuation was temporary and a ‘precautionary measure’, with staff remaining at the embassy in Tel Aviv and the consulate in Jerusalem.
Britons have already been advised against all travel to Israel and those already in the country have been urged to register their presence with the embassy.
The Foreign Office has also said land borders with Jordan and Egypt remain open, and consular teams are in position to provide assistance to British nationals who choose to leave Israel by land.
Minister for the Middle East Hamish Falconer said: ‘Our first job is to keep British nationals safe, and our dedicated teams in the region are working around the clock to do this.
‘We are asking all British nationals in Israel and the occupied Palestinian territories to register their presence so that we can share our updates with them and make sure we’re giving them the best advice possible.’