They are in IRAQI waters on a U.N. mandate. The mandate does not give them authorization to move into Iranian waters. It also does not specify that they need be in waters subject to a territorial dispute between Iran and Iraq, a fact the Brits are very aware of. Either they are incompetent sailors who blundered into disputed waters or they deliberately moved into disputed waters to provoke an incident or as a demonstration of their testicular endowments. Iran is making a mistake here in my opinion. The best thing for them to do would be announce they ship was not spying, release the sailors, and warn other countries to stay out of waters that are disputed unless those countries want to provoke an incident. This would put them in a good position and if any other ships entered those waters it would appear to all the world as a deliberate provocation.
John Thornton