The US ambassador to London has said the UK should join Donald Trump in adopting a hardline attitude towards Iran.

Britain and its European allies responded with dismay to the US president’s decision in May to pull out of the 2015 deal which relieved sanctions on Iran in return for an end to Tehran’s military nuclear ambitions.

The 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) and vow to protect European companies from US reprisals if they continue to trade with Iran.

London has made it clear it is committed to the JCPOA, but is open to talking to the US about ways to address shared concerns about Iran’s regional activities.

On Tuesday, the Foreign Office minister Alistair Burt said that the US had “not got this right” and Britain was ready to stand up to Trump, telling the BBC: “Sometimes you need to take a stand against friends.”

But the US ambassador, Woody Johnson, urged the UK to rethink its position.

In an article in the Sunday Telegraph, he said: “It is time to move on from the flawed 2015 deal.

Timeline Trump's rhetoric on Iran Show 'Nuclear holocaust' "They are going to be such a wealthy, such a powerful nation, they're going to have nuclear weapons," the Republican presidential frontrunner says. "They are going to take over parts of the world that you wouldn't believe and I think it's going to lead to nuclear holocaust." 'Dismantle' the agreement Trump says his "number one priority" is to dismantle the nuclear agreement. "This deal is catastrophic for Israel, for America, for the whole of the Middle East," he says. Iran 'playing with fire' The White House signals a tougher stance towards Iran, condemning a recent missile test and declaring America is putting the Islamic republic "on notice" following its "malign actions". Trump tweets: "Iran is playing with fire – they don't appreciate how 'kind' President Obama was to them. Not me!" 'Isolate' Iran Trump calls on all countries to "isolate" Iran, in a speech in Riyadh. "From Lebanon to Iraq to Yemen, Iran funds, arms and trains terrorists, militias and other extremist groups that spread destruction and chaos across the region," he declares. 'Rogue state' Trump says the nuclear accord is "an embarrassment to the United States". He tells the UN general assembly that Iran's government turned a "wealthy country with a rich history and culture into an economically depleted rogue state". 'Brutal, corrupt' regime Trump says it is "time for change" in Iran, after days of deadly protests against the government in Tehran. A day later he denounces the "brutal and corrupt" regime. Trump tears up deal Trump pulls the US out of the nuclear pact. Describing the deal as "defective at its core," he says: "Today, we have definitive proof that this Iranian promise was a lie. Any nation that helps Iran in its quest for nuclear weapons could also be strongly sanctioned by the United States." 'NEVER, EVER THREATEN THE UNITED STATES' Iran's president, Hassan Rouhani, tells the US it should not "play with the lion's tail" and warns that any conflict with Iran would be the "mother of all wars". Trump responds with an all-caps Twitter tirade: "NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE." 'Open' Trump says he is open to a new Iran deal, while confirming a return to sanctions. "I remain open to reaching a more comprehensive deal that addresses the full range of the regime's malign activities, including its ballistic missile program and its support for terrorism," he says in a statement.

“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.”

Johnson said the Tehran regime had used the flow of money coming in to the country since the easing of sanctions not to improve the lives of ordinary Iranians but 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.

“It is clear that the danger from Iran did not diminish in the wake of the deal,” he said. “It grew. Far from becoming a more responsible member of the international community, as we had all hoped, Iran grew bolder.”

He called for unity 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,” said the ambassador.

“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.”