THE US has told the UK to back Donald Trump over his tough stance on Iran or face "serious trade consequences".

Britain and its European allies were left disappointed in May when Trump decided to pull out of a 2015 agreement which relieved sanctions on Tehran if it eased nuclear ambitions.

Foreign Secretary Jeremy Hunt joined with his French and German counterparts last week to voice their "deep regret" at Washington's withdrawal from the Joint Comprehensive Plan of Action (JCPOA).

Whitehall made clear it was committed to the JCPOA but was open to talking to the US about ways to address shared concerns about Iran's regional activities.

Now ambassador Woody Johnson has urged the UK to rethink its position in a Sunday Telegraph article in which he said: "It is time to move on from the flawed 2015 deal.

"We are asking global Britain to use its considerable diplomatic power and influence and join us as we lead a concerted global effort towards a genuinely comprehensive agreement.

"The President has been explicit: any businesses that put their commercial interests in Iran ahead of the global good will risk serious consequences for their trade with the US."

Mr Johnson said the Tehran regime had used the flow of money coming into the country since the easing of sanctions to beef up spending on the military and networks of proxy forces and terrorists.

He accused Iran of launching cyber attacks against Western democracies, sponsoring Hezbollah terrorists in Lebanon, arming militants in Yemen and publicly threatening to destroy Israel.

Mr Johnson added: "It is clear that the danger from Iran did not diminish in the wake of the deal.

"Far from becoming a more responsible member of the international community, as we had all hoped, Iran grew bolder."

He called for a "united front" among Western nations to force Tehran into a change of course.

"Only by presenting a united front can we exert the maximum possible pressure on the Iranian regime, and get it to finally change course and put an end to its malign and reckless activities both at home and abroad.

"If the regime does make tangible and sustained changes to behave like a normal country, America is prepared to resume full commercial and diplomatic relations.

"Iran will be free to develop advanced technologies and play a full role in the global economy.

"Until then, America is turning up the pressure and we want the UK by our side."