Britain is sending a second warship to the Gulf to protect its oil tankers from Iranian gunboats. HMS Duncan, a destroyer currently in the Mediterranean, will join HMS Montrose, a frigate, next week.

Britain is on the edge of becoming involved in a conflict in which it can only deploy limited forces, but it could become the target of Iranian retaliation for any US escalation of the conflict.

In a sense, this may have already happened, if the US was indeed behind the royal marine commandos taking over an Iranian oil tanker allegedly bound for Syria off Gibraltar. It is difficult to take seriously the British claim that they carried out such a provocative act solely because of a request from the Gibraltarian authorities and in order to enforce EU sanctions on Syria.

The Iranians are demanding that the British release the Grace 1 tanker and it is probable that Iranian boats harassed the British Heritage tanker as an act of retaliation. An Iranian official warned the UK not to get involved in “this dangerous game”.

But Britain is already involved in the dangerous game and it is possible that the Iranians may find it less risky to act against Britain, whom they denounce as a US proxy, than directly against the US.

Tensions high as Trump approves new Iran sanctions: In pictures Show all 17 1 /17 Tensions high as Trump approves new Iran sanctions: In pictures Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, their surface-to-air missile is seen as it shoots down a US surveillance drone EPA Tensions high as Trump approves new Iran sanctions: In pictures This photo shows US RQ-4A Global Hawk unmanned surveillance drone. A drone of this model was shot down by Iran on Thursday 21 June AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures An oil tanker is on fire after it was subject to a suspected attacked at the Gulf of Oman on June 13. The US has blamed Iran for the attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures US President Trump holds up a signed executive order to increase sanctions on Iran on 24 June AP Tensions high as Trump approves new Iran sanctions: In pictures Iranian President Rouhani stated in a televised address that the White House is "afflicted by mental retardation" following the increase in sanctions on 25 June EPA Tensions high as Trump approves new Iran sanctions: In pictures An Iranian navy boat tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures A screenshot from a video released by the US Department of Defense that the US claims to show Iranian removing an unexploded limpet mine form the hull of the Japan-owned ship that was attacked in the Gulf of Oman on June 13 Getty Tensions high as Trump approves new Iran sanctions: In pictures An item reportedly found on the Japan-owned oil tanker that was attacked on June 13 in the Gulf of Oman AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures A handout photograph from the US Department of Defense shows a composite material that the US claim was left behind on the hull of the Japan-owned oil tanker following the removal of an unexploded limpet mine Getty Tensions high as Trump approves new Iran sanctions: In pictures A view from the cabin of an Iranian navy boat as it tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack EPA Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The picture suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The pictures suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack EPA

As in Iraq after 2003 and Afghanistan after 2006, Britain is becoming engaged in a conflict in which it is only a bit player, but must cope with the same dangers as the US. Some commentators seek comfort by recalling that a coalition of western maritime powers protected Kuwaiti tankers during the tanker war in the Iran-Iraq war in the 1980s.

At that time, it was Iran that was isolated, while today it is the US and Britain who are short of reliable allies who will do more than cheer from the side lines – as Israel and Saudi Arabia are likely to do. Already the United Arab Emirates is backing away from a confrontation with Iran, saying that is unclear if Iran placed small mines on tankers off the UAE coast in June, and it is drawing down its military forces in Yemen.

Iraq is at heart on the side of Iran as the only other significant Shia-majority power, while Qatar has its own long-term confrontation with Saudi Arabia. EU and other states will be dubious about President Trump – the great disrupter – taking on the role of a coalition builder and will be nervous of where he may be leading them in the Gulf.

From the British point of view, the crisis in the southern Gulf has parallels with Britain’s involvement on the US side in the invasion of Iraq in 2003. It is making itself a target without knowing where the US is heading and to what extent Trump – along with his more hawkish lieutenants – are prepared for a limited or full-scale war with Iran. The furore over former UK ambassador to the US Sir Kim Darroch’s forced departure from Washington shows just how limited Britain’s influence is in the White House.

From the Iranian viewpoint, a slow-burn crisis just below the level of outright warfare may be the least bad option. It is an improvement over waiting for Iran to be slowly strangled by economic sanctions which are Trump’s favourite method of putting pressure on enemies and friends alike.