As I posted in other threads about this. It is an act of war against the UK. Time to bomb the bastards back to hell.
I guess the Iranians will claim the British vessels had entered Iranian waters...
Other than that, I agree with the bombing comment.
But it isn't going to happen. It didn't happen in 2004 when Royal Navy and Marines were seized. It becomes a diplomatic incident. It all depends how the Iranians want to play it? The last time they made the UK military personnel apologise on TV and released them without their boats equipment. They have also detained U.S. naval contractors and released them too after confiscating their equipment.
No C-in-C is going to start a war over this sort of incident.