Sir Keir Starmer reneged on his refusal to let the US use UK bases for strikes on Iran. Photo / Chris Ratcliffe, Bloomberg
It was 5.25am on Sunday in London when Donald Trump issued his latest ultimatum to the Iranian regime.
After the US-Israeli strikes on hundreds of Iranian targets the previous day – including the missile that took out Ayatollah Khamenei – Iran’s interim leadership threatened to retaliate against Western targets with “the most intense offensive operation” in history.
The US President hit back with characteristically blunt force: “THEY BETTER NOT DO THAT, HOWEVER, BECAUSE IF THEY DO, WE WILL HIT THEM WITH A FORCE THAT HAS NEVER BEEN SEEN BEFORE!”
That message marked the beginning of what would become a day of turmoil and debate in Downing Street. It would ultimately lead to British Prime Minister Sir Keir Starmer changing his mind about the UK’s role in Trump’s war.
Ministers did not order the UK Armed Forces to participate in the US strikes and, on Sunday morning, were keen to urge de-escalation, and even keener to avoid debate about whether they were legal.
Asked about the legality of the attack on the morning broadcast round, John Healey, the British Secretary of Defence, replied: “That is for the US to set out and explain. It’s not for me, as Defence Secretary of the UK. I’m here to speak for the UK.”
In reality, there was already a fevered debate in Whitehall about what red lines the UK should set.
Legal advice from Lord Hermer, the Attorney-General, had established that joining a pre-emptive attack on Iran by Israel and the US was likely to be illegal, as would allowing them to use RAF bases in the region to carry it out.
In the run-up to the US strikes, the UK had denied repeated requests from the White House to use two bases – RAF Fairford in Gloucestershire and Diego Garcia in the Chagos Islands – in their plans for a strike on Iran. That refusal had last month cost the Prime Minister Mr Trump’s support for his Chagos deal to hand over British sovereignty of the islands to Mauritius.
The view of the UK government’s legal establishment was that only “defensive action” to protect the interests of Britain and its allies would be allowed under international law. There would be no involvement in pre-emptive strikes, nor participation in an offensive designed to result in regime change.
When the US-Israeli strikes began on Saturday morning, RAF jets from Britain’s bases in Cyprus and Qatar were launched into the skies to protect them from retaliatory Iranian drone and missile attacks. The aircraft did not strike Iran directly.
My statement on Iran. pic.twitter.com/Ki4VVTYO4N
— Keir Starmer (@Keir_Starmer) February 28, 2026
Twenty-four hours later, however, with the mullahs openly threatening Western forces in the region, the legal calculus was about to shift.
The increasing rhetoric from Tehran, combined with a fresh request from the White House and Pentagon to use British airbases, prompted a rethink in No 10.
The White House had asked again to use Diego Garcia to attack sites involved in launching strikes at regional allies. The request was for “specific and limited defensive action against missile facilities in Iran”, according to a summary of the UK’s legal position published late on Sunday.
This request did not fit neatly into the UK’s legal advice. Was it defensive to help the US launch pre-emptive strikes on Iranian facilities that would almost certainly be used to attack the UK?
Or did that tip over into an offensive attack that Sir Keir had vowed to avoid?
Much of the day in Downing Street was spent debating the pros and cons of accepting the US request.
On the one hand, there were obvious legal concerns about allowing Britain to facilitate strikes on Iran. Officials were conscious that the UK would be legally culpable for any illegal strikes if it had “knowledge of the circumstances”, under a UN ruling from 2001.
The Prime Minister, Lord Hermer and other ministers had always maintained that the UK should remain on the right side of international law. The Attorney-General’s previous legal advice, issued in June last year, banned Britain’s involvement in US strikes on Iranian nuclear facilities for the same reason.
Then there was the geopolitical risk. Ministers were keen to avoid mission creep, or risk the UK being dragged into a drawn-out Middle Eastern war that could end the same way as the Iraq war.
As Yvette Cooper, the Foreign Secretary, put it: “One of a whole range of calculations is, we know that there has been history in the past of regional escalation.”
The only current government official who was serving in 2003 was Jonathan Powell, Sir Keir’s national security adviser, who was Sir Tony Blair’s chief of staff when he decided to follow George W Bush into Iraq.
Powell was understood to be a key player in No 10 as the debate raged on Sunday, and as the Americans waited for an answer.
On the other hand, there were increasingly compelling reasons to think the UK should help the US to strike Iran.
First among them, according to Downing Street officials, was the large number of British civilians in the region who were at risk from Iranian strikes.
A Downing Street spokesman acknowledged on Monday that a “change in the situation” on the ground had played a part in No 10’s rethink.
Iranian drone and missile strikes had hit hotels and airports used by British holidaymakers and expats, many of whom have flocked to the United Arab Emirates in recent years.
The Foreign Office had estimated the number of Britons in the Gulf, especially in Dubai, where flaming missile debris hit a hotel on Saturday, at around 300,000.
With airspace over most of the region closed to civilian traffic, officials were working up plans to evacuate British nationals by road into neighbouring countries, but it was preferable to avoid the missile strikes in the first place.
There had also been a near-miss at a US naval base in Bahrain on Saturday. Hundreds of British personnel were stationed 200m from the successful Iranian missile and drone attack.
Secondly, as the attacks continued, ministers were acutely aware that Britain’s place in the international order was at stake in its response to the attacks.
Then there was the risk to the special relationship, already teetering because of weeks of debate about Diego Garcia and the Chagos Islands.
Other Arab countries were also demanding a tougher response from No 10, including Britain’s allies Bahrain, Qatar and the UAE.
Those countries were desperate to see Iran’s missile capability destroyed at source, and some called Sir Keir on Sunday and “asked him to do more to defend them”, according to a Downing Street spokesman.
In the end the Prime Minister, characteristically, took the decision with allies rather than going it alone.
The first hint of an about-turn from No 10 came at 8.18pm, when reports of an E3 meeting of the leaders of Britain, France and Germany emerged from Berlin.
A joint statement issued by the three countries said they would support “necessary and proportionate defensive action to destroy Iran’s capability to fire missiles and drones at their source”.
Confirmation from Downing Street did not emerge for another 40 minutes. In a hastily filmed five-minute video from inside No 10, Sir Keir said that the White House had “requested permission to use British bases for that specific and limited defensive purpose”.
He said: “We have taken the decision to accept this request – to prevent Iran firing missiles across the region, killing innocent civilians, putting British lives at risk, and hitting countries that have not been involved.”
In plain language, The Daily Telegraph understands that Starmer agreed to the US President’s request on the condition that the list of targets was agreed in advance, and that they were limited to strikes on ballistic missile depots and ballistic missile launchers.
The summary of government legal advice published confirmed that the UK would be “solely focused on ending the threat of air and missile attacks against regional allies unlawfully attacked by Iran and who have not been involved in hostilities from the outset”.
The Prime Minister’s decision to join pre-emptive action against Iran appeared to be vindicated just three hours later when one of the regime’s drone attacks on RAF Akrotiri in Cyprus hit its mark and detonated on the runway.
MoD analysts believe the drone was launched before Starmer’s video, and the attack, which happened just after midnight on Monday, should not be read as a retaliation by Iran. Hezbollah, the Islamist terror group and Iranian proxy in Lebanon, has claimed responsibility for the hit.
Trump would later tell The Telegraph that Starmer “took far too long” to change his mind about allowing America to use British bases because he was “worried about the legality”.
However, Sir Keir’s shift in policy will ultimately please the US President, and should give him a reprieve after weeks of criticism of the UK from the White House. It will also bolster London’s position among regional allies.
But there is deep concern in government about the legal and geopolitical risk posed by the conflict, and a reluctance to be drawn further into a long, complex war.
Trump said on Sunday that the US strikes are likely to continue for four weeks, the same length of time as Bush said his “major combat operations” in Iraq would last in 2003.
Bush was proven right with his calculation for that initial invasion, but the war lasted another nine years.
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