The article heric recommends is worth looking at. Here's an interesting quote:


A 1937 treaty gave Iraq full rights to most of the Shatt al-Arab and fixed the border on the Iranian shore. Iran resented the terms, maintaining it accepted them only under pressure from the British. Lingering bitterness over the treaty may have influenced last week's Iranian action.

"The fact that British forces were involved made the (latest) incident especially sensitive for Iran," says Simon Henderson of The Washington Institute for Near East Policy. "Iran resented this display of British dominance."


(Me again). There are layers upon layers of history in this region - and some of it does not reflect well on Britain and the US, from my limited knowledge of the whole thing ...