Last week, the UK’s ambassador to Tehran Rob Macaire was detained by Iranian authorities. He was returning from a commemoration of the 176 individuals killed on board Ukraine International Airlines flight 752, shot down by the Islamic Revolutionary Guard Corps, which mistook the passenger jet for a US missile. Mr Macaire had every right to attend the vigil, not least because four of the dead were British. Instead of issuing an immediate apology, Tehran absurdly claimed that Mr Macaire was orchestrating anti-regime demonstrations. <a href="https://www.thenational.ae/world/mena/britain-s-envoy-to-iran-leaves-tehran-on-pre-planned-visit-1.964704">The British ambassador was later declared persona non grata</a>. His effigy was burned by pro-regime protesters and a leading ayatollah called for him to be "chopped to pieces". In recent years, London has shown Tehran considerable goodwill. Iran was very fortunate that the UK reopened its embassy in August 2015, only one month after the Iranian nuclear deal, the Joint Comprehensive Plan of Action, was struck. This was a significant gesture, considering that London closed its embassy in 2011 after protesters illegally entered the premises, ransacked the compound and set fire to the Union Jack. Yet, London’s goodwill was met with disdain. In 2016, the British-Iranian national Nazanin Zaghari-Ratcliffe was arrested while visiting her family in Iran. Denied a fair trial, consular representation and only limited access to her daughter, Zaghari-Ratcliffe remains locked up in inhumane conditions. Other British nationals have also been detained, most recently academics Kameel Ahmady and Kylie Moore-Gilbert in August and September 2019 respectively. Then there was last summer's incident with the <em>Stena Impero</em>, a British-flagged vessel, which was illegally impounded by the IRGC as it was sailing through the Strait of Hormuz. This was a deliberate and cynical ploy by Tehran to have its own ship released from British custody in Gibraltar after it was sequestered for attempting to circumvent international embargoes on the Assad regime in Syria. With the exception of the odd public rebuke, London has shied away from forthright action against Iran. However, the UK needs to demonstrate that it will not be bullied by an international pariah. Not only will a tougher stance give the UK greater leverage in securing its interests abroad and the safety of its citizens in Iran, but it would also show that despite leaving the EU, the UK still has a voice in international affairs. Last week, Britain together with France and Germany triggered the JCPOA's dispute mechanism after Iran broke from the deal in the wake of the US assassination of Qassem Suleimani. Meanwhile, Prime Minister Boris Johnson correctly asserted that <a href="https://www.thenational.ae/world/europe/boris-johnson-let-s-do-a-trump-deal-to-replace-iran-nuclear-accord-1.964162">it was time for the JCPOA to be replaced</a> by a new US deal. However, Downing Street should also announce that it will have no part in Instex, the European initiative for an alternative payment system that would avoid US sanctions on companies doing business with Iran. London should also follow the US lead and designate the IRGC a terrorist organisation for its countless outrages across the globe. Needless to say, the UK should close its embassy in Tehran. Britain also needs to be more proactive in order to secure the release of British nationals detained in Iran. Just like crime syndicates and terrorist organisations that take hostages to extort money, Tehran is using British hostages like Ms Zaghari-Ratcliffe as leverage for the release of £400 million (Dh1.90 billion) that the UK owes due to an incomplete arms deal, scuppered by the 1979 Revolution. London can’t just hand over the cash as it would be in breach of EU sanctions. Also, Iran would no doubt simply use the money to fund more nefarious activities overseas. The best way for the UK to get its hostages released is to take away the financial incentives of keeping them detained and to make their imprisonment a financial liability. Back in March 2019, London issued Ms Zaghari-Ratcliffe “diplomatic protection”. This means that her case is no longer only a consular issue, but a diplomatic dispute between two states. It also means that Britain can and should take Iran to the International Court of Justice to seek a ruling that calls not only for her release, but also the payment of damages. If a recent US court order, which ruled that Iran pay compensation to journalist Jason Rezaian, who was detained in Iran for 544 days, is anything to go by, this figure could run into the hundreds of millions of dollars. Tehran would not be able to ignore such a verdict because last February the ICJ ruled in its favour, ordering the US to pay the so-called Islamic Republic $2 billion in frozen assets. If Iran ignores the ICJ on detained British nationals, it would delegitimise its own financial claims against the US. After the UK brings the Zaghari-Ratcliffe case to the ICJ, London should extend diplomatic protection to other citizens held in Iran and state that no funds will be released as long as its citizens languish in Iranian jails. The UK should also lend its full support to countries such as France, Sweden, Canada, Australia, Netherlands and Austria, all of which also have nationals unfairly jailed in Iran. London needs to abandon its gentle approach towards Iran. Not only would this help British security and the fate of its citizens languishing in Iranian jails, but it might also give the UK some much needed standing in world affairs as it prepares to leave the EU. <em>Simon Waldman is an associate fellow at the Henry Jackson Society and a visiting research fellow at King'’s College London</em>