An Iranian proverb maintains that if you trip over a pebble, you should remember it was put there by a Briton. It is hardly surprising that the crisis is proving fertile ground for Iranian conspiracy theorists.

“It was a British trap that we fell into,” a well-travelled and multilingual Iranian businessman sighed with conviction.

Britain, according to the theory, wants to put Iran under pressure on one of its most sensitive territorial issues – the Shatt al-Arab waterway, which forms the historical, racial and religious divide between Persians and Arabs and has been disputed for centuries.

The Royal Navy had deliberately used the 15 as bait for the Revolutionary Guards naval units, according to the theory. Why else were they so exposed so far from HMS Cornwall, their mother ship?

The Iranian businessman pointed out suspiciously that the British invariably referred to the body of water by its Arabic name, the Shatt al-Arab, rather than its Iranian one, the Arvand Rud (river). And he argued that once the Britons are freed, Britain will encourage Iraq to raise this territorial issue and back Baghdad for a settlement in Iraq’s favour. “It’s a typical British policy of divide and rule,” he said.

Another conspiracy is that Britain wanted to provoke a crisis to soften up Western public opinion for increased pressure against Iran, including possible American military action. “People are saying that three years ago, during a similar incident, British forces were shown blindfolded but there was little reaction from Britain,” an Iranian academic in the region told The Times.

“This time we see the British being held smoking and eating on television and London is saying ‘it’s intolerable’. People are asking: ‘Why the inconsistency?’ I don’t necessarily agree with this theory but I’m not dismissing it out of hand.”

Sir Richard Dalton, Britain’s former Ambassador to Iran, responded with clear exasperation. “My advice to the Iranians who used to give me that kind of c*** is that they’ve got to wake up and smell the coffee,” he told The Times.

Historically, Iranians have some ammunition for viewing Britain as perfidious. It was a British-inspired coup, engineered by MI6 with the CIA, that in 1953 toppled Mohammad Mossadegh, the popular Prime Minister, two years after he nationalised Iran’s oil industry, which had been controlled by Britain.

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