If the Iranians can hold uniformed military personnel, bearing recognizable insignia, operating under a formal command structure, carrying out a legal mission sanctioned by the United Nations, etc, as "spies;" then what's to stop Britain from detaining every and any Iranian official they can get their hands on, diplomats included, as "spies"?
I was thinking the same thing. There is another thread where the Iranians are threatening to hold a trial and execute the 15 British soldiers. If they do that, then the 15 Iranians that do get rounded up by Britian should be executed, too.