Conservative shadow foreign secretary Dame Priti Patel has called on the UK government to back the US if it attacks Iran.
US President Donald Trump has not publicly said whether the US will join the Israeli strikes.
But the BBC’s US partner CBS reported he had approved attack plans for Iran although he has not made a final decision on whether to strike the country.
Britain’s top legal adviser Lord Hermer has reportedly raised concerns privately that international law may only support UK involvement if UK personnel are targeted.
Dame Priti has argued the UK cannot “hide behind legal advice at a time of crisis”.
But Liberal Democrat leader Sir Ed Davey called for any legal advice to be published, adding: “The last thing we need is for the UK to be dragged into another illegal war in the Middle East by the US.”
Foreign Secretary David Lammy has travelled to Washington to meet his US counterpart Marco Rubio, after Donald Trump said he was considering whether to join Israeli strikes against Iran.
Meanwhile, Iran’s foreign minister Abbas Araghchi has confirmed that he will hold talks about the escalation of their nuclear programme with his counterparts from the UK, France and Germany and insisted his country was committed to diplomacy.
Speaking on BBC Breakfast, Dame Priti said said “we should be working with our allies, working alongside the US and Israel” and her party would support assisting the US in Iran.
She said: “If the US came to the UK and said ‘we need your assistance’, through use of our bases or even re-fuelling aircraft, obviously we would support that, my party would support that, working with the government and basing that on private discussions obviously based on intelligence, legal advice, security information.”
She stressed that strikes have taken place “to degrade Iran’s nuclear capabilities and their ballistic missile capabilities, which are a threat to us in the UK”.
However, there are reports the Attorney General Lord Hermer has privately raised questions over whether Israel’s actions in Iran are lawful, which would restrict the government’s ability to support any US action.
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.”
Israel has justified its war by claiming that Iran’s nuclear weapons programme poses an “imminent” and “existential” threat – although Iran claims the programme is peaceful.
The two countries have been exchanging fire for days after air strikes, which Tel Aviv said were aimed at preventing Tehran from developing a nuclear weapon.
The UK helped defend Israel from Iranian missile and drone strikes during a confrontation last year.
Asked if Lord Hermer was right to sound a warning, Dame Priti told Times Radio she believed the UK should support its “biggest ally”.
She said: “I don’t think we can hide behind legal advice at a time of crisis and national security when we have to work alongside our biggest ally in the world, the United States, when they look to us for potentially… setting out operational activities through our own military bases.”
Earlier, on BBC Radio 4’s Today programme, Dame Priti pointed out that embassy staff have been evacuated from Israel.
“There are thousands upon thousands of British nationals in Israel and currently the government response is not sufficient,” she said.
“There are [phone] numbers being put up for families to call and that is simply not good enough.
“We do know embassy personnel are being evacuated. And if they can do that for embassy staff then clearly additional facilities must be extended to British nationals in Israel.”
Dame Priti added other countries were offering air, sea and land options.
US ambassador to Israel Mike Huckabee said Washington was working to get military, commercial, charter flights and cruise ships for evacuation.
Dame Priti’s call for repatriation flights comes after the Foreign Office issued advice on Sunday against all travel to Israel.
British nationals currently in those areas have been told to register their presence via an online form and to follow the advice of local authorities.
The Foreign Office said international land border crossings with Jordan and Egypt remains open – with consular teams in place to provide assistance – while the embassy in Tel Aviv and consulate in Jerusalem remains “fully staffed”.
On Wednesday, a “rapid deployment team” arrived in Jordan which the Foreign Office said would “boost our consular presence”.