Iran has released two hostages, but others remain – and nuclear talks are on a knife edge | Sanam Vakil

Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori's return home is a step forward, but UK-Iran tensions are far from resolved

The long-awaited release from detention in Iran of two UK-Iranian dual nationals, Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori, signals, on the face of it, a constructive turn in UK-Iranian relations. It was brought about by the tireless behind-the-scenes work of advocates and officials , from progress in the Vienna nuclear talks to support from the Omani government and an international public pressure campaign.

Yet, despite this step forward, more challenging issues between Tehran and Whitehall are looming. Not least is the fear that by paying its 40-year-old 400m debt to Iran, the British government risks vindicating Iran's use of hostage-taking. It is for this reason that since Zaghari-Ratcliffe's detention, the British government has been rightfully reluctant to link the prospect of her release to the debt. Indeed, in 2016, then US president Barack Obama was heavily criticised for a similar repayment of $400m to Tehran after the release of four US-Iranian dual nationals. To comply with sanctions and counter-terrorism and money laundering regulations - and to prevent a repeat of the Obama optics - the Foreign Office has announced that the UK debt money has been ringfenced, and will be used for humanitarian purposes only.

Sanam Vakil is a senior research fellow in the Middle East and North Africa programme at Chatham House