Is this, some will be wondering, 2003 all over again?

In 2003 Britain joined the US in a highly controversial military campaign against Iraq in a quest to rid it of its supposed arsenal of “weapons of mass destruction”. These turned out to have all been destroyed years previously.

As America’s closest but junior ally, Britain is almost certain to be affected in some way by what happens now in the Middle East. If Donald Trump decides to commit US forces to help Israel eliminate Iran’s nuclear programme then what role will the UK be asked to play?

First off, Britain is very far from being a central player in this fight between Israel and Iran.

The UK, along with other G7 allies, has called for de-escalation, but Israel is unlikely to be listening.

This is not just because relations between Britain and Israel have recently soured after the UK joined other Western nations in sanctioning two Israeli cabinet ministers for inciting violence against Palestinians in the West Bank.

It is also because Israel had clearly decided that now was a window of opportunity to act militarily against Iran’s suspect nuclear programme and that the time for talking was over. (In an apparent snub to the UK, Israel reportedly did not inform it in advance of its attack on Iran, considering it “not a reliable partner”.)

But the UK still has a diplomatic role to play, together with its European allies who helped draft the 2015 JCPOA Iran nuclear deal that introduced intrusive UN inspections of Iran’s facilities in exchange for sanctions relief, until Donald Trump pulled the US out of the deal in 2018.

David Lammy, the foreign secretary, is in Washington meeting his US counterpart, and he will be heading to Geneva, Switzerland, on Friday to join his French, German and EU counterparts in talks with Iran.

The UK also has military and strategic assets in the Middle East and Indian Ocean.

Here’s how these could be involved.

This tiny, tropical Indian Ocean island base, jointly operated by the UK and US and now leased from nearby Mauritius, has a strategic significance out of all proportion to its size.

At 2,300 miles (3,700km) from Iran, it is a potential staging base for the USAF B2 Spirit heavy bombers.

These are the only aircraft in the world configured to carry the GBU-57 Massive Ordnance Penetrator (MOP) bomb. This 30,000lb (13.6 tonne) monster is sometimes referred to as a “bunker-buster” but that’s an under-estimate. Retired US Army General Petraeus referred to it this week as “a mountain-buster”. It is thought to be the only weapon powerful enough to penetrate deep underground at Iran’s suspect nuclear enrichment facility at Fordo.

If the US were to use Diego Garcia it would need permission from the UK. The Attorney General, Richard Hermer, is reported to have advised the UK government that any UK military involvement needs to be purely defensive in nature to remain within the law.

The B2 bombers have a range of nearly 7,000 miles, roughly the distance from their airbase in Missouri to Iran, and with inflight refuelling the US could, if it chose, bomb Fordo without using Diego Garcia.

The UK has two major strategic assets on this Mediterranean island.

One is RAF Akrotiri, currently home to a reinforced presence of RAF Typhoon jets. The other is the secretive Signals intelligence listening station on a mountain top at Ayios Nikolaos, known as “Ayia Nik”, and part of Britain’s Sovereign Base Area on Cyprus.

The British Army has also long used Cyprus as a base for its “spearhead battalion”, a rapid deployment force available for contingencies in the Middle East.

The RAF’s Typhoons are already engaged in Operation Shader, monitoring and occasionally bombing the Islamic State group (IS) and al-Qaeda bases in Syria and Iraq.

Last year, during a brief conflict between Israel and Iran, UK warplanes were reported to have helped shoot down incoming Iranian drones heading for Israel. But in this conflict an Israeli spokesperson told the BBC that no UK assistance has been sought or offered in doing the same thing.

The Royal Navy has had a small but vital role to play in keeping the Gulf and the Strait of Hormuz free from sea mines.

This dates back to the 1980-88 Iran Iraq tanker war, where mines were deployed and the UK activated its “Armilla Patrol”. Royal Navy minesweepers were based in Bahrain, an asset much appreciated by the adjacent US Navy’s 5th Fleet HQ which surprisingly, has been weak on mine counter measures.

However, the UK’s vessels have been nearing the end of their working lives and the Royal Navy presence has been gradually reduced. This has contributed to the depressing assessment that should Iran decide to choke off the Strait of Hormuz, through which flows 20-30% of the world’s oil supplies, its effect would be considerable.

The Ministry of Defence says that one Royal Navy minesweeper, HMS Middleton, is now in the Gulf. “Royal Navy vessels in the Gulf are currently at sea”, it adds, “and have not been retasked to undertake combat operations”.

There is also a small, 100-strong UK military presence in Iraq and a port facility at Duqm in Oman.

Iran has signalled on several occasions that any nation that attacks it, or which it judges to have helped enable an attack, will be retaliated against, sometimes referred to as “blowback”.

Top of the target list would be the US bases up and down the region, as well as its naval ships at sea.

But in the event that the UK were to authorise the USAF to use its base at Diego Garcia for an attack on say, the Iranian nuclear facility at Fordo, then that retaliation would almost certainly include the UK.

In practice, this could include ballistic missiles fired at RAF Akrotiri but here in Britain the Security Service, MI5, will also be on the alert for any hostile acts by Iran that could include sabotage and arson carried out by criminal gangs.