I'm not sure I would mess with the British. I have nothing to back this up, and I know they kind of got bitched a little bit in WWII with all the bombing and what not, but I really think Iran's seizure of 15 British sailors who were allegedly in Iranian waters (a claim the Brits dispute) could end very badly for them.
Can't you just see like four or five stodgy old British military guys in basement near Downing St., sipping tea, and just muttering "right, cheerio then, suppose we'll have to nuke them; terrible nuisance, this." I can.
Related thought . . . if these guys had done this to Americans (i.e., taken them hostage on what appear to be trumped up charges of trespass), I think a lot of people (myself included) would support a pretty viscious response. Iran ought to be careful here, because as of today the American people have zero appetite for another fight; but this kind of pointless, aggressive stuff strikes me as foolish, as it is really the only way to get people rallied against them.