Britain should side with Donald Trump rather than Brussels over Iran, the US ambassador to London declares on Saturday as he calls on America's "closest ally" to reverse its position on the controversial nuclear deal.

Writing for The Telegraph, Woody Johnson challenges the UK to abandon its European neighbours who are still backing a deal to trade with Iran and join forces with America to enforce hard-hitting sanctions.

Mr Johnson also delivers an explicit ultimatum to British companies, telling then to stop doing business with Iran or face "serious consequences" for your trade with America.

The comments are a direct challenge to Theresa May's Government coming days after a minister point-blank refused to go along with President Trump's sanctions on Tehran and keep the 2015 nuclear agreement alive.

They also come just six days after British foreign secretary Jeremy Hunt signed a joint statement with the EU which promised to push ahead with blocking the impact of the sanctions.