... Lord Howell, a former Conservative cabinet minister and chairman of the Lords international relations committee, asked his government on Thursday whether it was such a good idea to raid the Iranian oil tanker in Gibraltar in the first place. He said: Obviously we want to stop oil getting to President Assad, although probably he can get all the oil he wants from Russia. Are we not supposed to be on the same side as the Iranians on the question of nuclear proliferation and control? Can we have a firm assurance that we did this not just at the say-so of the US? Lady Goldie, for the government, insisted the request to intercept the ship came from the government of Gibraltar, but Foreign Office officials in the past have indicated the biggest factor in play was pressure from the US.
Speaking on the BBC, Nathalie Tocci, the special adviser to the EU foreign policy chief, Federica Mogherini, put the UK decision in a wider political context. The UK is feeling its own fragility and a fear of isolation as it tries to cut off its membership from the EU. Theres a line connecting the Iran story and the UK ambassador to the US.
Either way, once Grace 1 had been seized, UK shipping in the Gulf was in Iranian crosshairs. By the weekend, the British government was privately advising British flagged vessels not to carry oil through the Gulf, leading to an abrupt about-turn of a BP tanker, British Heritage, heading to collect oil in Basra. By Tuesday night the British government was lifting the code alert to level 3, the highest possible, and on Wednesday the giant British Heritage was interrupted by Iranian ships.
Curiously, media briefing about British Heritage, and the intervention by HMS Montrose, which warded off the Iranian boats by aiming its guns at them, came originally from the US, and not the Ministry of Defence...
https://www.theguardian.com/politics/2019/jul/11/is-the-us-nudging-britain-into-dangerous-waters-with-iran