Boris Johnson, who became the United Kingdom's newly elected prime minister on July 23, is a hard-line euroskeptic politician. While Europe is keenly following how Britain's Cabinet would proceed with Brexit under Johnson's leadership, in the Persian Gulf, Iranians are concerned about the fate of the Iran nuclear deal, or the Joint Comprehensive Plan of Action, in the post-Brexit era.

Will Johnson toe US President Donald Trump's line? If so, will Britain's withdrawal spell doom for the deal?

The UK-Iran relationship has been like a roller-coaster ride, with many ups and downs. In the 40 years since the Iranian Revolution, also called the Islamic Revolution, the two countries have severed ties as well as mended them.

Despite the ebbs and flows, British conglomerates British Petroleum and Royal Dutch Shell have never missed an opportunity to profit from Iranian oil.

The UK's Iran policy has been quite consistent with that of the European Union. Although the UK sent troops to Iraq in 2003, the British administration under then prime minister Tony Blair joined France and Germany to talk Iran out of a nuclear plan.

In 2015, when David Cameron was the prime minister, the UK was a major party at the negotiation table on the Iran nuclear deal. After Cameron stepped down in 2016, his successor, Theresa May, grappling with Brexit negotiations, managed to put up a united front with the EU and major European powers such as France and Germany.

In 2017, after President Trump announced his plan to pull the United States out of the deal, May and her counterparts in France and Germany flew to Washington, DC, to convince him to not ditch the deal.

To their disappointment, on May 8, 2018, the Trump administration officially withdrew from it. In addition, the US imposed an embargo on Iran's oil. Consequently, the UK held talks with France, Germany and Iran to find a solution to evade the American sanctions.

Which side will a post-Brexit UK take? Will it remain a fence-sitter or side with the US? This is a tough question facing Boris Johnson. Since Johnson's administration is eager to decouple with the EU, it is plausible to assume that he has no intention to work with the EU on the Iran nuclear issue.

Johnson will face stiff opposition from both the Labor Party and British companies if he wants topull Britain out of the deal.

The deal, brokered by the administration of former US president Barack Obama, was signed by the US, the UK, Germany, France and Russia, and approved by the United Nations Security Council. Iran agreed to halt its nuclear program in return for a lift of international sanctions.

Iran has been pushing the UK, France and Germany to bypass the long-arm jurisdiction imposed by the US.

Upset that the European nations were paying only lip service to its requests, Iran threatened to increase its uranium enrichment to 5 percent－h(huán)igher than the 3.67 percent limit defined by the deal－if the three failed to honor their promise.

If the UK were to exit the treaty, the deal would be hanging by a thread. "A UK withdrawal (would be) the final nail in the coffin for the Iran nuclear deal," said an Iranian commentator.

If the deal meets its demise, Iran will have no choice but to resort to its nuclear strength. Faced with a neighbor with growing nuclear muscle, Israel will not sit by idly, which could lead to a dangerous situation.

The author is former Chinese ambassador to Iran and senior researcher at the Chongyang Institute for Financial Studies of Renmin University of China. The views do not necessarily reflect those of China Daily.