Britain negotiated the original Iran deal in 2015 with France, Germany, China, Russia and the US in a process coordinated by the European Union. The Tehran regime agreed to curb its nuclear program in return for the lifting of sanctions.
But Trump pulled out of the deal, which was struck by his predecessor Barack Obama, three months ago because Trump believes it is not stopping Iran from meddling the Middle East. Hard-hitting economic sanctions were reimposed last week with more to come in November.
“America is turning up the pressure and we want the UK by our side,” Johnson 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.
“Together, we can help bring about the peace and prosperity in Iran that the whole world wants to see.”
Johnson urged British businesses to cut ties with Iran. The UK’s trade with Iran was £365 million ($640 million) in 2016.
“The President has been explicit: any businesses which put their own commercial interests in Iran ahead of the global good will risk serious consequences for their trade with the United States,” Johnson said.
“Only by presenting a united front can we exert the maximum possible pressure on the Iranian regime and get them to finally change course and put an end to their malign and reckless activities both at home and abroad.”
The call amounts to a plea for Britain to break with its European Union partners over Iran and adopt Trump’s strategy.
The UK is set to be formally out of the EU in April 2019, assuming a Brexit deal can be arrived at. But on Sunday senior UK government figures rejected the demands, further deepening the policy rift between the two traditional allies.
One minister said Trump was simply throwing “red meat” to his support base, and his strategy would be counter-productive, while a Foreign Office source reiterated the UK’s support for the agreement.
The minister added: “The trouble is with this approach is that it plays into the hands of the hardliners [in Tehran]. They court this. The whole purpose of the deal was to allow big companies to go into Iran – which is crying out for infrastructure improvement.
“It is all ratcheting slightly out of control – I can’t see Britain wanting to join in with that because where it takes you into a more hardline position.
“We pride ourselves on having a better understanding of the world than most – we would urge absolute caution on this. This is not the direction of travel you want go in.”
A Foreign Office source said: “We remain committed to the deal and are open to talking with the US administration and Congress about ways we can work together to address our shared concerns about Iran’s regional activity.”
In recent months Britain has thrown its support behind a so-called “blocking statute”, implemented in the EU headquarters of Brussels, which will protect European business from America’s Iran sanctions. The move is an attempt to keep European companies trading with Iran – seen as a critical factor in keeping the agreement alive.
Iran has said it will stick with the deal only if it continues to enjoy the economic benefits it was promised.
In the statement signed on Monday by Foreign Secretary Hunt, his French and German counterparts Jean-Yves Le Drian and Heiko Maas, and Federica Mogherini, the EU foreign policy chief, they say they “deeply regret” the US sanctions and “are determined to protect European economic operators engaged in legitimate business with Iran.”
Asked the following day if Britain would “go along with the US” on Iran, Alistair Burt, a Foreign Office minister, said: “We made it clear that we regard the nuclear deal as an important part of the region’s security.
“We think this is really important, sticking to a deal a number of partners have agreed to.”
Asked how British companies could protected from US sanctions, he added: “If a company fears legal and enforcement activity, they can be protected by EU legislation. But the practicalities might be different. Many companies won’t be affected.”
Challenged over whether the UK would “stand up” to President Trump, Burt said: “They can expect us to do that – yes. Sometimes you need to take a stand against friends.”