Well this will be good for the stability of the Middle East.  With U.N. approval, British Navy personnel have been stopping and boarding ships in Iraqi waters to search for supplies being smuggled from Iran to the Iraqi insurgents.  Earlier today, shortly after stopping and searching a merchant ship, the British suddenly found themselves surrounded by Iranian naval vessels.  The British were detained and escorted into Iranian territorial waters.

Navy personnel captured at gunpoint (The Scotsman Evening News):
...A journalist on board the ship, Ian Pannell, said that they had just boarded a dhow, a traditional Arabian sailing vessel.

Mr Pannell said: “While they were on board, a number of Iranian boats approached the waters in which they were operating – the Royal Navy are insistent that they were operating in Iraqi waters and not Iranian waters – and essentially captured the Royal Navy and Royal Marine personnel at gunpoint."...

Basically a large British naval vessel (in this case the HMS Cornwall) stops a passing ship, and then sends over teams of inspectors, in this case two small inflatable boats with a total of 15 British sailors and marines.  It's not clear but it sounds like the British may have completed the inspection when the Iranian vessels surrounded the two small inflatable boats and forced the sailors and marines to return with them to Iranian waters.  Details are sketchy at this point, and I haven't heard any news reports explaining why the Iranians captured the British, but presumably the claim will be that the British were in Iranian territorial waters.

Iran has been promising to respond to the capture of Iranian diplomats in Iraq, which has happened more than once.  The Iranian President has not been mincing words in his rhetoric--the holocaust was a myth, Israel should be wiped off the map, the US and Britain are enemies of Iran, etc.  Not surprising I suppose, our President hasn't had sunny things to say about them either... "axis of evil" and all that.

The last time Iran seized British Navy personnel the British men were held for 3 days, blindfolded, and displayed on Iranian television.  Considering how much more tense things are right now with the Iranians enriching uranium (and likely supporting the Iraqi insurgency), this was not exactly a bright move on their part.  All it does is strengthen the position of American and British hardliners who think a war with Iran is inevitable and necessary.

It looks like today is not going to be a good day.