Britain's most modern warship was last night racing towards the Persian Gulf as military experts warned it was only a matter of time before Iran launched a guerilla warfare-style attack on shipping.

Defence chiefs ordered HMS Duncan, a £1 billion destroyer bristling with missiles and carrying the latest anti-submarine technology, to break off from NATO exercises in the Black Sea and head to the Strait of Hormuz to protect UK-flagged oil tankers.

The Type 45 vessel, also carrying elite Royal Marine Commandos and a Merlin helicopter, will initially join HMS Montrose, which last week trained its guns on boats suspected of belonging to Iran’s Islamic Revolution Guard Corps when they tried to impede British Heritage, an oil tanker owned by BP, as it moved into the strait.

The oil tanker British Heritage pictured in Rotterdam, the Netherlands. This week five Iranian boats tried to stop the ship as it approached the Strait of Hormuz. A British warship trained its guns on the boats and gave them a warning

A fifth of the world’s oil passes through the strait, which is just 21 miles wide at its narrowest point and the only sea passage from the Persian Gulf to the open ocean.

It has become the focus of mounting tension between Iran and the West, triggered by the decision of US President Donald Trump last May to abandon a nuclear deal with Tehran and subsequently impose a raft of sanctions.

HMS Duncan, which has a crew of 190 Royal Navy officers and sailors, is expected to join HMS Montrose on patrols along international shipping channels off the Iranian coast this week.

The increase in Britain’s military commitment comes despite warnings from Iran not to play President Trump’s ‘dangerous game’ – and as Tehran demands the release of Grace 1, an Iranian-owned oil tanker seized off Gibraltar by British Royal Marines earlier this month amid evidence it was carrying oil to Syria in breach of EU sanctions.

In an apparent bid to ease tensions, Foreign Secretary Jeremy Hunt last night told his Iranian counterpart that Grace 1 could be released. Mr Hunt tweeted that he had spoken to Iranian Foreign Minister Mohammad Zarif and added that the tanker could be allowed to depart if assurances were received from Iran that its cargo would not be delivered to Syria.

Colonel Richard Kemp has said that Iran will continue to seek revenge until the Grace 1 (pictured on July 4 when it was arrested) is released from Gibraltar. He also said an attack is a matter of when, not if

HMS Montrose trained its guns on five Iranian boats (left, an analysis of the warship) and the Royal Navy's most modern warship (right, an analysis of the warship) was last night speeding towards the Persian Gulf

Colonel Richard Kemp, a former UK Armed Forces commander, last night warned that while Grace 1 remained in custody in Gibraltar, Iran would continue to seek revenge and the Royal Navy needed to be prepared to respond.

‘The next time there is a stand-off in the Persian Gulf, the Royal Navy must send the strongest possible signal to Iran,’ said Colonel Kemp, who has chaired the UK’s Cobra emergency response committee.

‘Unquestionably it is a matter of when, rather than if, Iran launches another attack. Only if they are met with very stiff resistance will they get the message.’

Britain last year withdrew two Merlin helicopters, which had been used for decades to monitor threats to international shipping in the Persian Gulf, from their Omani base at Al Musannah, close to the strait.

The Merlins, which use sonar sensors to identify enemy submarines, were considered surplus to requirements in the Gulf and were transferred to a task force intended to protect the UK’s new aircraft carrier HMS Queen Elizabeth.

The decision was made in spite of Iran’s investment in a fleet of 23 mini-submarines which are armed with torpedoes and difficult to detect while laying mines.

A diagram showing recent military movements and attacks in the tense Middle East region

A formation of US Avenger-class mine countermeasure ships. They were photographed in the Arabian Sea on July 6 this year. Defence expert Colonel Hamish de Bretton-Gordon said he was concerned that a mistake or misinterpretation of intention in the Persian Gulf could trigger a bigger clash with Iranian forces

A UK soldier on board the Grace 1 after it was arrested off Gibraltar. The UK decided to stop the tanker as it was thought to be heading to Iran, in breach of EU sanctions

Defence expert Colonel Hamish de Bretton-Gordon said he was concerned that a mistake or misinterpretation of intention in the Persian Gulf could trigger a bigger clash with Iranian forces. He said: ‘There are so many pieces on the chessboard and so many antagonists facing each other.

‘I think it is very worrying that more shots could be fired before this is resolved.

‘For its part, it is essential for Britain to play its role as the US’s critical friend to ensure sound judgment on our side, while militarily we must back the US to the hilt.’

HMS Duncan was last night understood to be approaching the Suez Canal from where it will sail south through the Red Sea at speeds of around 20 knots before heading east through the Gulf of Aden towards Iran.

The warship, which entered service in 2013, is considered one of the most advanced in the world.

It carries Royal Marines from Juliet Company of 42 Commando who are trained to board and take control of boats in situations similar to that which saw the detention of Grace 1.

Lieutenant Max Chapman, from Juliet Company, said: ‘My team are highly trained in the dangerous operations to gain access to and take control of vessels attempting to avoid interdiction.’

Last night the MoD said: ‘As part of our long-standing presence in the Gulf, HMS Duncan is deploying to the region to ensure we maintain a continuous maritime security presence.

‘This will ensure that the UK, alongside international partners, can continue to support freedom of navigation for vessels transiting through this vital shipping lane.’