Well the Iranians are emboldened by the pathetic response from the Brits when their sailors were captured by the Iranian Navy in 2007. The proper response would be a complete cut of diplomatic ties followed by the sinking of an Iranian naval vessel. The Iranians are likely expecting an apology from simpering David Cameron.
Yeah, its not like Americans have ever been taken hostage by Iranians....
Cameron is probably wondering to what extent, if any, Obama will back the Brits..