Its not really a threat if you can't back it up

From The New York Times:

LONDON, March 27 — Tensions escalated between Iran and the West on Tuesday over 15 Britons held by the Iranians, with Prime Minister Tony Blair warning that Britain’s campaign to free them would move into a “different phase” if they were not released.

[. . .]

Mr. Blair told GMTV television on Tuesday that Britain was trying “to make the Iranian government understand these people have to be released and that there is absolutely no justification for holding them.”

“I hope we manage to get them to realize they have to release them,” he said. “If not, then this will move into a different phase, but at the moment what we’re trying to do is make sure that that diplomatic initiative works.”

Officials in his office and at the Foreign Office insisted that he was referring specifically to a tougher diplomatic posture, not to military or other more confrontational means. The American naval exercises in the Persian Gulf were scheduled long before the British soldiers were seized, so the timing is coincidental.

Margaret Beckett, Britain’s foreign secretary, who is visiting Turkey, phoned her counterpart in Tehran on Tuesday and “spoke in very robust terms reiterating the U.K.’s concern about the continued detention of our personnel,” a Foreign Office spokesman in London said, speaking in return for anonymity.

I think that we can see here what the outlines of the "different phase" will be. I fully expect the British to move from "robust terms" to the full deployment of "harsh language" very soon if these servicemen aren't returned.

It wasn't always like this. In the old days of the British Empire a full military expedition would already be assembling to give the Iranians a spanking that they would never forget. Even as recently as the Thatcher era this kind of provocation would have been met with overwhelming force. But now the British have neither the will nor the ability.

I know that the timing of this is centered on the UN's vote to place some mostly hollow sanctions on the Iranians over their nuclear weapons program, but the choice of British sailors and Marines rather than American is due largely to the British government's decision to draw down its forces in Iraq.

There is an old saying in the Middle East, "a falling camel attracts many knives". Blair's decision to get out of Iraq was seen as weakness by the Tehran regime and to a culture which believes that the best possible time to kick someone is when they are already down that made British forces an irresistible target.