At the end of the day, the only people who can say for sure what happened are the RN and the Iranian crews involved.
Going by the BBC map on the other page, the Shatt al-Arab waterway is outside HMS Cornwall's AoO. Maybe they
were on a sneeky-beeky mission and were actually in Iranian waters. Maybe they
were in Iraqi waters and the Irianians were just playing silly buggers to get back at Blair & Bush's economic restrictions.
Even with the 'conclusive proof' that UKGovt is going to publish, I doubt the Iranians or the Anti-Blair nuts in this country will believe that we weren't on some spy mission or pre-invasion recce.
The Iranians are renowned for being somewhat impish over the protection of their waters. The Strait of Hormuz is the only available waterway for oil leaving the Arab Gulf states. Thing is it is located between the UAE and Iran. The Iranians have a delightful tendancy of pouncing on tankers that might stray into Iranian waters whilst passing through the Strait and holding them for weeks or even months whilst they are searched for weapons or spies! As a result, another tanker is needed to take up the slack in supply which bumps up the price at the pump.
I could ramble on but I wont.
