BORIS Johnson is being urged to hold firm and stand by the international nuclear agreement with Iran after Donald Trump urged him and Britain’s European allies to “recognise reality” and abandon the “very defective” deal.

The SNP and the Liberal Democrats last night urged the Prime Minister to reject the US President’s “dangerous” call; a move they suggested would further isolate Iran and lead to an escalation in the Persian Gulf crisis.

At a White House press conference, Mr Trump said the "time has come" for Britain, Germany, France, Russia and China to "break away" from the Joint Comprehensive Plan of Action [JCPOA].

Under the 2015 deal, Iran agreed to limit its nuclear programme and allow in international inspectors in return for the easing of economic sanctions. Tehran has always denied it is seeking to build nuclear weapons.

The President made clear that he would not allow Iran to having nuclear weapons. He said the JCPOA expired shortly and gave Tehran a “clear and quick path to nuclear breakout”. He went on: “Iran must abandon its nuclear ambitions and end its support for terrorism.

"The time has come for the United Kingdom, Germany, France, Russia and China to recognise this reality. They must now break away from the remnants of the Iran deal - or JCPOA - and we must all work together towards making a deal with Iran that makes the world a safer and more peaceful place," he added.

Just hours before Mr Trump's remarks, Mr Johnson made clear the deal remained the "best way of preventing nuclear proliferation in Iran".

He told MPs during Prime Minister's Questions: "It is the best way of encouraging the Iranians not to develop a nuclear weapon and after this crisis has abated, which of course we sincerely hope it will, that way forward will remain.

"It is a shell that has currently been voided but it remains a shell into which we can put substance again," declared the PM.

Last night, Mr Johnson held talks over the phone with Justin Trudeau, his Canadian counterpart, with Downing St saying they discussed the need for de-escalation on all sides.

A spokesman added: “On the nuclear deal, the leaders committed to continue working together and with international partners to ensure Iran is prevented from acquiring a nuclear weapon.”

The SNP’s Alyn Smith said: “The UK Government must robustly reject Donald Trump’s dangerous calls to ditch the Iran nuclear deal – successfully negotiated between the international community and Iran – and instead set out a clear commitment to reviving the JCPOA.

“All efforts must be made to de-escalate and instead engage in diplomatic efforts to prevent this crisis from tipping over the edge.”

The Stirling MP said the UK Government, rather than walking away, must press ahead with efforts to bring Iran and the US back to the table to rescue this deal “or risk further escalation and violence”.

He added: "The UK Government cannot simply pander to the Trump administration's demands. It must mount a robust defence of international law and pursue diplomatic efforts to bring the chaos to a peaceful conclusion."

Ed Davey for the Liberal Democrats echoed the point, saying: “Trump’s call for the UK to break away from the Iran nuclear deal is dangerous, and Britain should reject it.

“It’s time for Boris Johnson to decide where his values lie. It is essential the UK stands up for international law and human rights. He must not allow the UK to be used as the lapdog of President Trump and should remember that the Iran nuclear deal was signed by an American President, whose strategy of diplomatic engagement worked with Iran.”

The party’s acting leader added: “Rather than rejecting the nuclear deal, Britain should be calling on Trump to get back to the table. With our European allies, we must do all we can to de-escalate this situation and return to dialogue with Iran.”