Nazanin Zaghari-Ratcliffe’s fresh jail term is a signal that Iran will detain her until the UK resolves a long-running debt dispute with Tehran, her husband has said.

Richard Ratcliffe said on Monday he fears his wife is facing an “open-ended detention” after she was sentenced to an additional year’s imprisonment and a further year-long ban on leaving Iran.

Mr Ratcliffe said the development “hit us hard”, with the British-Iranian charity worker having already completed a five-year sentence on widely-denied allegations levied by Iranian authorities.

Her lawyer Hojjat Kermani said she received the second sentence on a charge of spreading “propaganda against the system” for participating in a protest in front of the Iranian Embassy in London in 2009.

Prime Minister Boris Johnson said the fresh sentence was “cruel, inhumane and wholly unjustified”.

Some observers have linked Mrs Zaghari-Ratcliffe’s detention to a long-standing debt the UK owes Iran.

Britain is thought to owe the nation as much as £400 million over the non-delivery of tanks in 1979, with the shipment stopped because of the Islamic revolution.

Mr Ratcliffe told BBC News: “It’s certainly a hard place to be.

“I think it’s a signal that is an open-ended detention until the debt-issue is solved.”

He said his wife informed him of the latest sentence in a phone call on Monday morning. She is yet to be summoned to jail, with her lawyer appealing the verdict, Mr Ratcliffe added.

Ministers have said Britain continues to “explore options” to resolve the debt dispute, but insisted the “two issues cannot be merged into one”.

Mr Johnson tweeted: “Iran’s decision to sentence Nazanin Zaghari-Ratcliffe to another year in prison is cruel, inhumane and wholly unjustified. She must be allowed to return to her family in the UK and we will continue to do all we can to get her home.”

His comments were echoed by Foreign Secretary Dominic Raab, who said: “This is a totally inhumane and wholly unjustified decision.

“We continue to call on Iran to release Nazanin immediately so she can return to her family in the UK. We continue to do all we can to support her.”

Mr Johnson also said that the Government will be “working very hard” to secure her release.

“The Government will not stop, we will redouble our efforts, and we are working with our American friends on this issue as well,” he told reporters.

Mrs Zaghari-Ratcliffe’s MP Tulip Siddiq said the “terrible blow” showed the Government’s efforts to secure her release have “clearly failed”, as she called for an urgent explanation from ministers.

“It is devastating to see Nazanin once again being abusively used as bargaining chip,” the Hampstead and Kilburn representative said.

In 2016, Mrs Zaghari-Ratcliffe was detained on charges of crimes related to national security, and was sentenced to five years’ imprisonment.

She completed the latter part of her sentence under house arrest due to the coronavirus crisis in March, but was returned to court later in the month where she was tried on new charges of “spreading propaganda against the regime”.

Rupert Skilbeck, the director of Redress, the human rights group supporting Mrs Zaghari-Ratcliffe, said she had never received a fair trial in Iran, and was innocent of the allegations made against her.

“Nazanin has already suffered severe physical and psychological impacts from the torture and ill-treatment she has been subjected to during the past five years,” he added.

“A further sentence to prison or house arrest may cause irreparable damage to her health.

“Her detention has always been illegal under international law.

“The case must be dismissed and she should be allowed to return to her husband and daughter in the UK immediately.”

Former foreign secretary Jeremy Hunt questioned why the issue of an IMS (International Military Services) debt had not been dealt with.

“This is so distressing. Iran’s cruelty seems to know no bounds,” the Conservative MP tweeted.

“Impossible to imagine what the family are going through today.

“Key question is why the IMS debt issue is still not settled given the UK accepts that it owes this money?”

The new jail term comes amid tensions in the Middle East over Iran’s nuclear programme, with the country abandoning all limits of its 2015 nuclear deal with world powers in the wake of former US president Donald Trump’s 2018 decision to unilaterally withdraw from the accord.

US President Joe Biden has expressed a desire to return to the deal if Iran honours limits on its nuclear programme.

During a call with Iranian president Hassan Rouhani last month, Downing Street said Mr Johnson had raised Mrs Zaghari-Ratcliffe’s case and Iran’s breaches of its nuclear deal, the Joint Comprehensive Plan of Action (JCPOA).

A Number 10 spokesman said Mr Johnson had “stressed that while the UK remains committed to making the Iran nuclear deal a success, Iran must stop all its nuclear activity that breaches the terms of the JCPOA and come back into compliance”.