Richard Ratcliffe, the husband of the imprisoned British-Iranian dual national Nazanin Zaghari-Ratcliffe, has described a Boris Johnson premiership as a potential threat to national security.

Ratcliffe, who is on hunger strike outside the Iranian embassy in London to protest against his wife’s continued detention by Tehran, said: “Johnson’s failure to take responsibility for his own mistakes makes me question his ability to protect our security.”

He said his protest was getting under the skin of embassy staff and leading to an increase in harassment.

Nazanin Zaghari-Ratcliffe's husband: I will join hunger strike for as long as I can Read more

Ratcliffe had earlier accused Johnson of making mistakes and false promises that enabled his wife’s Iranian jailers to discredit the case for her release.

Ratcliffe said a story in the Sun newspaper, written on the day he met Johnson as foreign secretary, had given him false hope and antagonised the Iranians.

The story claimed Johnson had won a Whitehall agreement to repay a £400m debt owed by the British government to the Iranians arising from the sale of Chieftain tanks in the 1970s.

He said the story turned out to be a bigger problem for her cause than an earlier mistake by Johnson at a foreign affairs select committee hearing, in which he said Zaghari-Ratcliffe had been teaching journalism in Tehran. Her family insist she was on holiday.

Ratcliffe said the mistake by Johnson at the hearing was still being used by Iranian news outlets to justify laying a second set of charges against her.

Facebook Twitter Pinterest Nazanin Zaghari-Ratcliffe was jailed for five years in Iran in 2016 after being convicted of spying, which she denies. Photograph: James Veysey/Rex/Shutterstock

His allies say the error at the hearing may have been off the cuff, but the Sun briefing was a considered decision by a senior political figure in the Foreign Office that raised expectations in Tehran, but served only to deepen the distrust of Johnson.

Zaghari-Ratcliffe’s MP, Tulip Siddiq, challenged Johnson to explain his role in possibly briefing that the UK government was prepared to t pay the £400m debt to Iran. She said: “If Boris Johnson claims that he or his team was not responsible for briefing the debt payment story then he should publicly deny it - as it seemed to be attempting to relieve the pressure caused by his own gaffe.

“If he did suggest that payment was imminent, Boris Johnson cruelly raised the hopes of the families involved and made matters much worse by failing to deliver.”

Ratcliffe, speaking on BBC radio, said: “Promises have consequences. Perhaps the bigger problem was when the press was briefed the money was going to be paid. Expectations were raised. He [Johnson] said no stone was going to be left unturned and obviously that did not happen. She remains in prison and others have been arrested, and so we have gone from ‘no stone unturned’ to ‘not my fault’.”

Johnson, in the BBC TV Conservative leadership debate on Tuesday, claimed his mistake at the select committee had made no difference, but he has never been asked whether he played a role in the briefing of the press about the repayment of the Chieftain tank debt.

The story in the Sun, marked “exclusive”, said Johnson and the chancellor, Philip Hammond, had authorised government lawyers to finally settle the 38-year dispute over the tank deal.

In fact, resistance in Whitehall, both in the Ministry of Defence and the Treasury, left Iran still fighting in the courts last month to recoup the money, as well as the outstanding interest.

Timeline Imprisonment of Nazanin Zaghari-Ratcliffe in Iran Show Hide Arrest in Tehran Nazanin Zaghari-Ratcliffe is arrested at Imam Khomeini airport as she is trying to return to Britain after a holiday visiting family with her daughter, Gabriella. Release campaign begins Her husband, Richard Radcliffe, delivers a letter to David Cameron in 10 Downing Street, demanding the government do more for her release. Sentenced She is sentenced to five years in jail. Her husband says the exact charges are still being kept a secret. Hunger strike Nazanin Zaghari-Ratcliffe's health deteriorates after she spends several days on hunger strike in protest at her imprisonment. Appeal fails Iran’s supreme court upholds her conviction. Boris Johnson intervenes Boris Johnson, then Foreign Secretary, tells a parliamentary select committee "When we look at what [she] was doing, she was simply teaching people journalism". Four days after his comments, Zaghari-Ratcliffe is returned to court, where his statement is cited in evidence against her. Her employers, the Thomson Reuters Foundation, deny that she has ever trained journalists, and her family maintain she was in Iran on holiday. Johnson is eventually forced to apologise for the "distress and anguish" his comments cause the family. Health concerns Her husband reveals that Zaghari-Ratcliffe has fears for her health after lumps had been found in her breasts that required an ultrasound scan, and that she was now “on the verge of a nervous breakdown”. Hunt meets husband New Foreign Secretary Jeremy Hunt meets with Richard Ratcliffe, and pledges "We will do everything we can to bring her home." Temporary release She is granted a temporary three-day release from prison. Hunger strike Zaghari-Ratcliffe is on hunger strike again, in protest at the withdrawal of her medical care. Diplomatic protection The foreign secretary, Jeremy Hunt, takes the unusual step of granting her diplomatic protection – a move that raises her case from a consular matter to the level of a dispute between the two states. Travel warning The UK upgrades its travel advice to British-Iranian dual nationals, for the first time advising against all travel to Iran. The advice also urges Iranian nationals living in the UK to exercise caution if they decide to travel to Iran. Hunger strike in London Richard Ratcliffe joins his wife in a new hunger strike campaign. He fasts outside the Iranian embassy in London as she begins a third hunger strike protest in prison. Hunger strike ends Zaghari-Ratcliffe ends her hunger strike by eating some breakfast. Her husband also ends his strike outside the embassy.

Moved to mental health ward According to her husband, Zaghari-Ratcliffe was moved from Evin prison to the mental ward of Imam Khomeini hospital, where Iran’s Revolutionary Guards have prevented relatives from contacting her. Daughter returns to London Zaghari-Ratcliffe's five year old daughter Gabriella, who has lived with her grandparents in Tehran and regularly visited her mother in jail over the last three years, returns to London in order to start school. Temporary release Amid the threat of the coronavirus pandemic, she is temporarily released from prison, but will be required to wear an ankle brace and not move more than 300 metres from her parents’ home. New charges Iranian state media reports that she will appear in court to face new and unspecified charges. In the end, a weekend court appearance on a new charge of waging propaganda against the state that could leave her incarcerated for another 10 years is postponed without warning, leading Zaghari-Ratcliffe to say "People should not underestimate the level of stress. People tell me to calm down. You don’t understand what it is like. Nothing is calm."

Ratcliffe is on hunger strike in solidarity with his wife, who is herself on hunger strike in a Tehran jail over the continued threats to impose a second set of charges against her.

Ratcliffe accused Tehran of using her jailing as a pawn in a wider diplomatic battle with the UK both over the tank debt and more broadly to press the UK to do more to support the Iran nuclear deal.

Asked if Johnson was wrong to say his words at the hearing had made no difference, Ratcliffe said: “Yes, of course they had consequences. The main difference they had is obviously they enabled a propaganda campaign that was run against Nazanin a couple of weeks afterwards, accusing her of being a spy and that the foreign secretary had proved it. It has very traumatic consequences for her.

“It was used to justify the second court case. It did not cause the second court case, but was used to justify it and has been used to discredit her ever since. A couple of weeks ago there was stuff on Press TV, an Iranian press outlet, again recycling his words, saying, listen, the foreign secretary confirmed she was there working when she was not.”

Jeremy Hunt, the current foreign secretary and a rival for the Tory leadership, refused to criticise Johnson, saying point scoring would be unseemly. “My job is to get her out,” he added.

• This article was amended on 21 June 2019 to correct the spelling of Tulip Siddiq’s name.