Until ten days ago, RAF Fairford was of little interest to anyone apart from a charmed circle of plane spotters who knew it had one of the longest runways in the country.

Now this obscure military airport near the Gloucestershire village of Whelford is at the centre of a growing crisis which threatens to grievously damage Britain’s relationship with our chief ally, the US.

Things came to a head on Sunday night when all 12 B-1 bombers based at Fairford were ordered to fly back to America immediately, with some leaving in such haste that they took off before the refuelling tankers that replenish their tanks in mid-air.

It later emerged that the order to evacuate Fairford came after the Pentagon reportedly received new threats about an Iran-backed plot against the base.

It has been the focus of fevered speculation about sabotage ever since Sunday, September 27, when five hooded and masked men were arrested shortly after midnight, having been seen acting suspiciously outside the perimeter fence.

It’s a sign of how closely the Americans were monitoring the situation that US President Donald Trump later pronounced himself ‘surprised’ when the men were given bail.

The issue is all the more sensitive because the planes are not only expensive – each B-1 cost well over $300million (£2237million) – but they are impossible to replace as they are not made any more, so the Pentagon cannot afford to lose one, let alone the 12 based at Fairford.

As there are only 45 B-1s still in service, the squadron at the Gloucestershire base represented a full quarter of America’s stock of its most potent strike aircraft.

Yes, they will now have to fly sorties from the US itself, with two or three crews on board to cope with the length of the trip and mid-air refuelling, but they clearly feel this is the price they have to pay for peace of mind.

Meanwhile, there will be rejoicing in Tehran over the decision to withdraw the bombers as it represents yet another success in its bid to push the US out of its air bases and intelligence hubs in Europe and the Middle East.

The Americans have already been forced out of Saudi Arabia, Bahrain and Kuwait – and pulled out of Iraq, too – following missile and drone attacks launched by hostiles often described as ‘local militias’ but which are almost certainly Iranian proxies.

However, these countries are all just across the Persian Gulf from Iran – or in the case of Iraq, next door – not 2,750 miles away in an island off mainland Europe.

The Americans will be asking themselves, if Britain cannot provide security at its air bases for Allied planes thousands of miles from Iran, what use will it be during a conflict with Russia?

The truth is there has been a sea-change in US attitudes to its traditional role in the defence of Europe in recent years.

Many younger Americans are from Latin America and Asia, and the Second World War story just doesn’t have the same hold on their imaginations as it did for those who had European roots. But the loudest voices calling for ditching Europe as a security priority and switching to Asia are Trump himself and Wasp securocrats like the Pentagon’s number two, Elbridge Colby, the grandson of former CIA director William Colby.

Another vocal advocate of an ‘America First’ foreign policy is Tucker Carlson, who has gone from being a bow-tie wearing Establishment supporter of Nato three decades ago to a full-throated supporter of the MAGA movement and, in particular, its distaste for ‘forever’ wars.

Carlson tells his huge online following that he sees no need for allies and no good in protecting them. Instead, America should concentrate on looking after itself.

All this leaves other British bases and European ones vulnerable. By far the most important of Britain’s overseas bases from the American point of view is Diego Garcia. While it’s nominally an RAF base, in practice it’s a US one. From this heavily guarded base in the Indian Ocean, America’s heavy bombers can reach across the Middle East – including Iran – to southern Russia.

The future of Diego Garcia has long been in doubt as the Labour government seems anxious to appease Mauritius over its claim to the Chagos Islands. Trump has traditionally been opposed to the giveaway but will he still be now? Might he not make a deal with Mauritius to get what Britain has given until now?

The Fairford farce looks as though it has given Iran a strategic win – and put another nail in the coffin of US-British co-operation.

Mark Almond is director of the Crisis Research Institute, Oxford.