One of the most senior Democrats in Washington has dismissed a key element in the west’s long standing strategy on Iran’s nuclear programme as “ridiculous”. His comments throw open the debate about how far the US and its partners should go in seeking a compromise with Tehran after on Friday’s presidential election.

John Kerry, chairman of the Senate foreign relations committee and the Democrats’ 2004 presidential nominee, told the Financial Times in an interview that Iran had a right to uranium enrichment – a process that can produce both nuclear fuel and weapons grade material.