In the warm blue waters of the Strait of Hormuz there is no room for mistakes. Its shipping lanes, which are only two miles wide, are packed with tankers carrying crude oil from the Gulf past implacable enemies: Iran on one side, the United Arab Emirates on the other.

A lethal strike by either side could be disastrous. That, it appears, is the assessment of the Royal Navy, which is to send 100 Royal Marines to protect British ships as attacks on oil tankers escalate, raising fears of a war with Iran.

This week America blamed Tehran for attacks on two tankers in the Gulf of Oman, on the approach to Hormuz. Analysts and diplomats fear a cycle of tit-for-tat violence that will be difficult