Britain's ambassador to the US said Donald Trump abandoned the Iran nuclear deal in an "act of diplomatic vandalism" because it was agreed by his predecessor Barack Obama, according to the latest leaked cables.

The Mail on Sunday published details of the dispatch from Sir Kim Darroch, despite a warning from Scotland Yard that journalists who released further details of the ambassador's communications could be in breach of the Officials Secrets Act (OSA).

The warning prompted a furious row over press freedom, with Tory leadership contenders Boris Johnson and Jeremy Hunt lining up to defend the right of the media to publish leaked government documents.

The latest memo to be disclosed was said to have been written by Sir Kim in May 2018 following a visit to Washington by Mr Johnson - who was then foreign secretary - in a last ditch attempt to persuade the Trump administration not to abandon the Iran deal.

Under the terms of the agreement - still supported by Britain, France and Germany - international sanctions on Iran were eased in return for Tehran accepting curbs on its nuclear programme.