Equation
Lieutenant General
First, release the tanker. The Iranians decided to claim it was not obeying "international rules" and still haven't given a detailed explanation as to what rules were broken. They've had enough time to come up with a bullcrap justification. It was an apparently empty tanker in Omanese waters heading for a Saudi port. If you're going to lie in a situation like that, do better than "it was being very naughty".
Second, provide evidence that their tanker wasn't in breach of the European sanctions the UK was acting under. If the evidence isn't accepted, offer that the tanker can be escorted closely/under supervision until the oil is off-loaded.
If the tanker is headed to Syria and would be breaking European sanctions, try a diplomatic argument that Iran isn't bound by them. Try the legal route before breaking the law in such a flagrant way.
We don't have enough there currently, but in theory it probably does in a place like the Gulf if it organised convoys. However, the RN ships are mostly on other duties and would take time to get there.
You're hilarious! Iran should de-escalate by releasing the British ship but the British shouldn't do that with Iran? Iran should go to your courts and waste their time over something you clearly had no right to do? Very very funny. What arrogance from a country far past its prime! The UK has no authority over Iran or any other country in any fashion under any circumstance. Your suggestion is as funny as saying that you have seized your neighbor's car because he used it to shop at a supermarket that you have sanctioned and you cried foul when he seized your car back; you insist that he should have went to your office to argue a legal case against you and your 3 friends as "judges" for why your sanctions don't apply to him and why he should have his car back in a few months! By your own logic, it is now Britain's turn to slowly wait for the charges and start a legal battle in Iran with Iranian judges for why the Stena Imperio did not violate any laws and should be released. Don't be in a hurry; I have a feeling the case could drag on for a couple months/years. Sound fair to you? Two wrongs don't make a right? Return that tanker then; it is the only thing for the British to do! Until then, Iran has every right to seize everything on the high seas with a British flag or owner to give the UK a taste of its own medicine and show it not to start things again without thinking about the consequences. If Iran was more well-connected like the US (in which case the UK would never even dare think about seizing a tanker from them), every Iranian ally should seize British ships too to show the UK what a barbaric business model its advocating for.