John Baron is MP for Basildon and Billericay.

The Joint Comprehensive Plan of Action, to give the Iranian nuclear deal its proper title, ranks as one of the more successful monuments to international diplomacy of modern times. Despite deep disagreements with Western nations on matters such as Libya, Iraq and Syria, Russia and China negotiated alongside their Western counterparts and played a valuable role in persuading the Iranian leadership to sign up to the deal’s requirements. This helped to resolve a festering sore in Iran’s international relations and calmed tensions in a febrile Middle East. Donald Trump would be well advised not to jeopardise it.

In considering what we have to lose if the deal fails, it is worth recalling how we got to the present situation. International concerns about a possible covert Iranian nuclear weapons programme were simmering throughout the early 2000s, and the hardline government of Mahmood Ahmadinejad did little to reassure the international community when Iran repeatedly defied UN Security Council Resolutions to halt the refinement of its stockpile of fissile uranium and – albeit legally – withdrew from voluntary elements of its safeguarding agreements with the International Atomic Energy Agency (IAEA). The standoff deepened in 2009 when it emerged that Iran had secretly constructed a large underground nuclear facility, out of sight of the international community.

Matters came to a head in November 2011, when the IAEA published a report with a small section detailing its concerns over ‘possible military dimensions’ to the Iranian civil nuclear programme. This heavily caveated section contained very little new information and no firm evidence of a nuclear weapons programme. However, many seized upon it as concrete proof that the Iranians were constructing an atomic bomb in defiance of its obligations under the Nuclear Non-Proliferation Treaty.

In Britain, the Government maintained that ‘all options were on the table’ to prevent Iran from acquiring this capability, and there was open and serious speculation about a joint US and Israeli air strike on Iran’s nuclear facilities, with British involvement or support, to ‘deal’ with this problem. As a mark of how high tensions were running, my Parliamentary debate in February 2012 mildly calling for the military option to be dismissed in favour of dialogue was defeated by 285 votes to 6.

Fortunately cooler heads prevailed, helped by the unexpected Presidential election victory during the following year of Hassan Rouhani. Having campaigned specifically on a platform of improving relations with the international community, and strongly supported by the large constituency of younger voters frustrated by Iran’s relative lack of economic progress and international isolation, Rouhani had a strong mandate.

This he used, together with positive messages from London, Washington and elsewhere, to sideline the hardliners in the Iranian establishment and restart the nuclear negotiations. The final result was the signing of the nuclear deal in 2015, which offered Iran sanctions relief in return for guarantees and other undertakings related to its nuclear programme over the next 10-15 years. In another positive sign, having been overrun by an angry mob in 2011, our Embassy in Tehran reopened in August 2015.

Hardliners in both Iran and the United States have never been fully content with the deal and, in the case of the latter, ensured that Congress requires the US President to certify every 90 days that Iran is not cheating on the agreement. Barack Obama did this on each occasion, as has President Trump twice since his inauguration. No signatory of the agreement believes Iran is in contravention of the deal, nor does the IAEA or indeed senior members of the Trump Administration.

If President Trump does de-certify the deal, as now appears increasingly likely, nothing immediately will change. It will pass to Congress, which has a 60-day window to decide whether it believes Iran is keeping to its obligations or not. Given the strength of feeling on the value of the deal, including from the leaders of the other countries which signed the agreement – Theresa May has certainly spoken to the President indicating Britain’s strong support for it – and from many inside the US foreign policy establishment, we can all hope Congress will not take this step.

However, even if Congress does endorse the President’s de-certification, this remains an internal legal matter within the United States. It does not affect the commitment to the deal of France, Germany, the United Kingdom, Russia, China and Iran. Nevertheless, it would invariably undermine the agreement which took so much time, painstaking diplomacy and political capital to achieve. It will also put paid to the great hope that a successful agreement could act as a foundation for better relations between Iran and the United States, which for so long have been blighted by faults and misunderstandings on both sides over the last 40 years.

In Iran, President Trump’s de-certification will certainly undermine and discredit President Rouhani, who has staked his political reputation on the success of the deal. It will work to the hardliners’ advantage, especially in the powerful Revolutionary Guard, who maintain that the West remains implacably opposed to Iran and that, as a result, any accommodation is naïve and not their country’s interests.

More broadly, the failure of the nuclear deal would send a very bad signal to the wider international community. World leaders, especially in countries such as North Korea, would surely consider such a failure as proof that such agreements with the United States are not worth the candle. This is not good for countries like Britain – or the United States, for that matter – which strive to uphold the rules-based international system. For all these reasons, I hope President Trump makes the right decision.