The husband of the jailed British-Iranian dual national Nazanin Zaghari-Ratcliffe has gone on hunger strike for a second time in an attempt to persuade the UK foreign secretary to do more to bring his wife back from detention in Iran. His hunger strike is to take place outside the Foreign Office in London.

Richard Ratcliffe took the radical step in desperation after the Iranian authorities said earlier this month that Nazanin had lost her appeal against a second prison sentence. She will return to jail for another year, and then subject to a travel ban for a further year after that.

She has already served a five-year sentence for spying. She was arrested in 2016 and has always protested her innocence.

Ratcliffe’s six-year-old daughter, Gabriella, lives with him in London, having returned from Tehran two years ago, where she had stayed with her grandmother while Nazanin was serving her jail sentence.

The new foreign secretary, Liz Truss, has spoken to both Nazanin and Richard since her appointment, but has not held out any hope of a breakthrough.

At issue between the family and the Foreign Office is the ministerial refusal to pay a GBP400m historical debt to Iran that the UK government acknowledges that it owes.

The Foreign Office says sanctions prevent the payment being made, but refuse to reveal what efforts it has made to make the payment, or why previous attempts at prisoner swaps involving British-Iranian dual nationals have failed. It has not set out which sanctions prevent the payment, or why a humanitarian gift cannot be made to Iran.

Explaining his decision, Ratcliffe said Truss, in conversation with him, “shared how angry she was, how she would speak with the Iranian minister. But it was not a trigger-point to act. That would be when Nazanin was returned to prison.

“For us, reimprisonment is too late. It would mean not seeing Nazanin until 2023.

“Just prior to the news, we had a very bleak meeting with the Foreign Office, ending with me telling them I had no confidence in their strategy and their reluctance to act: they still do not settle the debt to Iran whose impasse in 2016 caused Nazanin to be taken. There is no legal impediment now, the minister said.

“But also they do nothing to disincentivise Iran’s hostage-taking, still refuse to use the word ‘hostage’ despite promises to Nazanin. They still seem surprised each time Iran escalates – but it still happens cost-free. They still say the same slogans. At some point, soundbites don’t protect you”.

He added: “It can be difficult to capture the feeling of a life wasting away, watching prison creep closer while we sit in the PM’s in-tray. Nazanin was increasingly distraught last week.

“Two years ago I went on hunger strike in front of the Iranian embassy, on the eve of Boris Johnson taking over as prime minister. Two years ago we were allowed to camp in front of the Iranian embassy for 15 days – much to their considerable anger. But it got Gabriella home.

“We are now giving the UK government the same treatment. In truth, I never expected to have to do a hunger strike twice. It is not a normal act. It seems extraordinary the need to adopt the same tactics to persuade government here, to cut through the accountability gap.”

Ratcliffe’s MP, Labour’s Tulip Siddiq, said: “It should never have come to this. It’s time for the government to listen to the demands of Nazanin’s family, including paying the debt we owe to Iran, and finally bring her home.”

Rupert Skilbeck, the director of the NGO Redress, which is running a legal campaign for the release of Zaghari-Ratcliffe, said: “It’s deeply worrying that Richard has felt compelled to resort once again to a life-threatening measure to bring attention to the desperate plight of his family.

“Five years on, we have only seen setback after setback. The UK government’s approach is clearly not working. It’s time to stand up to perpetrators of hostage-taking by sanctioning those who perpetuate this reprehensible practice, and to bring Nazanin home.”