Iran has fired missiles at a joint US-UK base in the Indian Ocean as it warned British lives were “in danger” after prime minister Sir Keir Starmer backed the US to carry out further strikes.

Tehran directed two intermediate-range ballistic missiles at Diego Garcia in the Chagos Islands but neither hit. One of the missiles wasreportedly shot down by a US warship, while the other failed in flight.

It is undertood that the attack took place before Downing Street said on Friday that UK bases will now be used for US “defensive operations to degrade the missile sites and capabilities being used to attack ships”.

On Saturday, the minitry of Defence condemned the attack as “reckless”.

Diego Garcia is around 2,360 miles away from Iran and home to an airbase capable of accommodating long-range US bombers, with around 2,500 American troops based on the island.

The UK has agreed to cede sovereignty of the islands to Mauritius and lease back the base, in a move that has strained relations with Washington in recent months.

Diego Garcia is strategically valuable to the US, and has been used as a launchpad for operations in the Middle East for years, with Donald Trump describing the deal as a “big mistake”.

Why is there a UK-US base on Diego Garcia?

At the conclusion of the Second World War, concerns began to grow within the US administration that their access to overseas bases was diminishing, as more countries became independent from colonisation.

With naval planners concerned over the prospects of Russia and China getting a stronger foothold in the Indian Ocean, it was suggested that the Diego Garcia base would allow the US to project power in the region.

Given that the UK had established a base there during the war and it remained under their administrative status, it was decided in 1961 that the British government would detach the Chagos Archipelago from colonial Mauritius for future military use.

After secret negotations, the US agreed to make payments to the British of up to $14m for its use.

A report from Chatham House noted: “Since then, the military base in Diego Garcia has served as an anchor for American operations.

“The island hosts an extensive airfield with runways long enough to accommodate large military aircraft like B-52 bombers, KC-135 tankers, reconnaissance aircraft and transport planes. It also has major fuel storage facilities, radar installations, and control towers that can support regional military operations.”

During the 1991 Gulf War and the 2003 Iraq War, it was a critical launchpad for US air operations.

How will UK plans to hand over Chagos Islands to Mauritius impact the base?

The government has argued the deal is necessary to guarantee the future of the Diego Garcia base after an advisory International Court of Justice ruling in 2019 backed Mauritian claims to sovereignty over the islands.

Under the plan, the UK will pay £34.7 billion in nominal terms over 99 years to secure use of the base.

However, legislation enabling the handover has not progressed through Parliament since January 20, even though it is in its final stages.

The agreement has faced significant criticism in both Westminster and the White House, with parties such as Reform UK and the Conservatives heavily criticising the decision.

What has Trump said about it?

The £35 billion deal that includes a plan to lease back strategically important UK-US military base on Diego Garcia – the largest island within the remote Indian Ocean archipelago – has led to barbed exchanges at Westminster and abrupt changes of heart by the American leader.

While the US administration initially hailed the deal as a “monumental achievement”, Mr Trump subsequently lambasted it as an “act of great stupidity” and “total weakness”, amid transatlantic tensions over his ambitions to annex Greenland.

In a further reversal, the US president then signalled his support for the agreement, saying it was “the best” Prime Minister Sir Keir Starmer could make.

But he again recently withdrew his support for the accord branding it “a big mistake”, reportedly because Britain had refused the use of its military bases for a US strike on Iran.

The UK has stated it will not proceed with the deal unless it has the support of the US.

Speaking outside the White House on Friday, Mr Trump said: “It’s been a very late response from the UK.

“I’m surprised because the relationship is so good, but this has never happened before.

“They were really, pretty much our first ally, all over the world.”

Referring to Diego Garcia, he said: “They didn’t want us to use the island, the so called island, which for some reason they gave up rights to it.

“I was a little surprised in the UK, to be honest. They should have acted a lot faster.”

Why has Iran targeted the military base?

Although the attack came before the UK allowed its bases to be used by the US, it could be seen as a threat against the UK over such collaboration – while the range a sign of the potential of Iranian missiles.

Foreign minister Abbas Araghchi said Iran will “exercise its right to self-defence”.

Posting on X, he said: “Vast majority of the British People do not want any part in the Israel-US war of choice on Iran. Ignoring his own People, Mr Starmer is putting British lives in danger by allowing UK bases to be used for aggression against Iran.

“Iran will exercise its right to self-defence.”

Could Iranian missiles actually hit the UK base?

As the UK is drawn further into the conflict, some in Britain are naturally concerned about the potential for the fallout to reach the mainland.

This is very unlikely, experts say, as Iran’s offensive capabilities are not assessed as long-reaching enough to make the 3,000 mile journey.

Vuk Vuksanović, associate at foreign policy think tank LSE IDEAS, said: “There is no evidence that Iran has the capacity to attack the US or UK mainland.

“Iran, with its missile and drone capability, does have the capacity to strike US and UK military outposts in the wider Middle East, including the Gulf and the Levant.”

This includes the RAF Akrotiri base in Cyprus which has already been targeted by drones and the Diego Garcia base.

However, analysists had estimated that Iran’s longest-reaching weapon is the Khorramshahr 4 missile, which can potentially hit targets from 1,200 to 1,900 miles away.

Given that ballistic missiles have succeeded in being launched to the Chagos Islands, it is now feared that Iran is more capable than previously thought.