Iran's actions don't strike me as those of a nation avoiding war. I wonder if their leaders are actually trying to provoke American airstrikes? Unless the US Air Force launched an all-out campaign, airstrikes wouldn't do much damage to the Iranian nuclear program. It would also strengthen the Iranian government, rallying the support of the people behind it in a nationalistic fervor. It also would galvanize world opinion in support of Iran. Therefore, the US should under almost no circumstances strike first blow in this potential conflict. We lose the moral high ground if we do.
There might be an interesting dynamic to consider if Britain decided to strike Iran alone pending a failure to return (or worse) the British prisoners. Iran would be in a pickle at that point, because it lacks serious capability to further retaliate against Britain. That is, British troops aren't in vulnerable spots like American troops, and London is out of range of Iranian missiles. Iran would not want to escalate a conflict with a secondary opponent, exposing itself and playing its few good cards, when its primary opponent (USA) is right around the corner waiting for it to slip up. Not saying I advocate Britain starting a war, but if it came down to it, I'd rather the British launch the strike unilaterally without the US getting directly involved. It would give the West the strategic initiative.
It will most likely be a non-issue, though. Iran abducted British sailors once a few years ago and returned them after some grandstanding. I'm sure it will do the same this time around.