The Iranian ambassador to the UK has been told his country’s plan to press fresh charges against the British-Iranian dual national Nazanin Zaghari-Ratcliffe is “unjustified and unacceptable”. Zaghari-Ratcliffe, 42, was due to end her five-year imprisonment next spring. But the fresh charges throw that timetable into doubt. Hamid Baeidinejad was summoned to meet Thomas Drew, Foreign Office director general for the Middle East, North Africa, Afghanistan and Pakistan, on Thursday evening. He conveyed the UK’s “grave concern at this development and called for Iran to end her arbitrary detention”. A spokesperson said: “We have made it clear to the Iranian ambassador that his country’s treatment of Nazanin Zaghari-Ratcliffe is unjustified and unacceptable, and is causing an enormous amount of distress. “Iran is further tarnishing its reputation through its actions towards Nazanin. It is time to end her arbitrary detention and that of the other dual British nationals it is holding.” Zaghari-Ratcliffe had been released in the spring on a tag requiring to stay at her parents home in Tehran. The threat of a second trial was hanging over her for a month in what is seen as a move to ratchet up pressure on the UK. She has warned she cannot stomach a return to jail, and her family want greater signs that this will not be tolerated by the UK government. She has been detained in Iran since 2016, when she was sentenced to five years in prison over allegations, which she denies, of plotting to overthrow the Iranian government. This week the foreign secretary, Dominic Raab, also condemned her treatment as “unacceptable”. His comments came after her husband, Richard Ratcliffe, said the mother of one – who has been out of prison on furlough but under house arrest in Tehran since March due to the coronavirus crisis – was presented with a court summons on Tuesday. She was told to pack a bag to bring to Monday’s hearing, as she would be returning to prison after the court appearance, Ratcliffe added. Only months from her expected release date, Zaghari-Ratcliffe was returned to court in September and told she would face a second trial, but this was postponed at short notice with no future date set. Her husband said it would hear charges of spreading anti-government propaganda in a case officials dropped in December 2017, after a visit from the then foreign secretary Boris Johnson, but reopened in May 2018.