The attorney general has warned Sir Keir Starmer that Britain becoming involved in US attacks on Iran could be illegal.
Richard Hermer has reportedly called on the prime minister to limit the UK’s involvement in the conflict to solely protecting its allies from being attacked.
The government’s top legal adviser has questioned whether Israel’s actions in Iran are legal, while cautioning against British engagement unless UK personnel are targeted.
Lord Hermer is reportedly reluctant to sign off any offensive operations, with a source telling The Spectator: “The AG has concerns about the UK playing any role in this except for defending our allies.”
It comes after Donald Trump taunted Iran on Wednesday over the extraordinary prospect of US airstrikes on Tehran.
After Ayatollah Ali Khamenei rejected demands for unconditional surrender, the US president said: “I may do it. I may not do it.”
“The next week is going to be very big,” he teased as thousands fled the Iranian capital following the latest aerial bombardment, leaving many shops closed and streets empty.
Sir Keir chaired an emergency Cobra meeting on the Middle East crisis late on Wednesday, two days after he expressed confidence that Mr Trump would not join the unfolding war between Iran and Israel.
The Foreign Office has evacuated family members of embassy staff from Israel, but has not advised British nationals to leave the country.
Meanwhile Downing Street has maintained that Britain’s position is that it wants de-escalation, not escalation in the conflict.
Priti Patel said the Conservative Party would support the Government in joining the military fight against Iran if it was deemed necessary.
The shadow foreign secretary said the Tories want peace in the region, but “we're crystal clear that Iran should not be able to obtain nuclear weapons”.
“And if the Government judges that such action is necessary to avoid that then we would absolutely support the Government if it deemed it necessary to ensure that we can defend our country, our citizens and effectively a lot of our strategic equities in the Middle East region,” she told ITV’s Good Morning Britain.
And energy minister Miatta Fahnbulleh said Sir Keir will approach the issue with a “cool, calm head”. “What I will say is that we have a Prime Minister who is a lawyer and a human rights lawyer, he will obviously do everything that is in accord with international law,” she told Times Radio.
David Lammy is on Thursday set to meet his US counterpart in Washington against the backdrop of potential American involvement in the conflict.
The foreign secretary and Marco Rubio will discuss Mr Trump’s comments about potentially joining Israel’s strikes on Iran.
Israel and Iran have been exchanging fire for days after air strikes, which Tel Aviv said were aimed at preventing 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.
The Israeli military said Tehran and other areas of Iran were being targeted during the latest round of airstrikes on Thursday, warning people in a post on X 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.
Tensions are now ratcheting up between the US and Iran, with Supreme Leader Ayatollah Ali Khamenei rejecting Mr Trump’s call for surrender and warning that any American military involvement would result in “irreparable damage” to the US.
The Foreign Secretary’s talks in Washington will cover the deteriorating situation in the Middle East and the war in Ukraine, as well as the UK-US trade deal, parts of which were finalised by Sir Keir and Mr Trump at the G7.
Meanwhile, nuclear talks with Iran and senior diplomats from the UK, Germany and France as well as the EU will take place in Geneva on Friday, a European official said.
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”.
If the US decides to go ahead with strikes, it could seek to use the joint US-UK military base on Diego Garcia, which the UK would reportedly need to sign off on.
A spokesman for the attorney general’s office said: "By long standing Convention, reflected in the ministerial code, whether the law officers have been asked to provide legal advice and the content of any advice is not routinely disclosed.
"The Convention provides the fullest guarantee that government business will be conducted at all times in light of thorough and candid legal advice."
