A leaked letter to the UN Security Council shows that the British government has rejected the US position on Iran’s nuclear and conventional weapons programs, is siding with France and Germany at the UN, and is risking a diplomatic confrontation with its closest ally.

The letter, dated August 20, notifies the head of the UN Security Council that the ‘E3’ (Britain, France, Germany) remain ‘committed to fully implementing UNSCR 2231 (2015), by which the JCPOA [the ‘Iran deal’] was endorsed in 2015’, and that the United States request for ‘snapback’ on sanctions on Iran has no legal validity: ‘Germany, France and...