Downing Street has urged Iran to allow the family of a detained British-Iranian woman to visit amid fears that she is being tortured to sign a forced confession after she was moved to an isolated psychiatric ward.

Zaghari-Ratcliffe was moved to the mental health ward of Iman Khomeini hospital on Monday – a move that the family initially welcomed after months of calling for her to get medical treatment.

But her husband, Richard Ratcliffe, said he was now worried that she could be forced to condemn the British government and sign a “confession” after Revolutionary Guards holding her blocked access to her father and consulate staff.

The prime minister’s official spokesman told a Westminster briefing: “We are extremely concerned about Nazanin’s welfare and call for her immediate release, and we urge Iran to allow family members to visit her and check on her care.”

Before being transferred, Zaghari-Ratcliffe told relatives: “I was healthy and happy when I came to Iran to see my parents. Three and a bit years later and I am admitted to a mental health clinic.

“Look at me now – I ended up in an asylum. It should be an embarrassment. Prison is getting harder and harder for me. I hate being played in the middle of a political game. I just hate it.”

Her MP, Labour’s Tulip Siddiq, said Zaghari-Ratcliffe was “shackled like a caged animal” as she was taken from her cell to a psychiatric ward. Asking an urgent question in parliament, she said: “The family fear she may be drugged or being tortured and may be forced to sign a confession to unnamed crimes.”

Siddiq also asked what urgent steps the UK government had taken to establish the treatment Zaghari-Ratcliffe was receiving, adding: “What protests have the government made regarding the fact that Nazanin was shackled like a caged animal on her way to receiving urgent medical care?”

Earlier Ratcliffe said his wife’s hunger strikes in protest at her continued detention could have prompted the Iranian authorities to move her. But he is worried by what the Revolutionary Guards may do to her.

Speaking to the Today programme he said: “The last time she met the Revolutionary Guard, which was when she was on hunger strike, they were pressuring her to sign various denouncements of the British government and to confess to various things. That’s when I began to get worried … Are they only isolating her again to squeeze her?”

When it was pointed out that few outside Iran would believe any forced confession she made, Ratcliffe said: “I think that’s right – just getting her home is the most important.”

He said: “We were quite hopeful when she was being transferred to hospital. We’ve been calling for a long time that she get medical treatment. So we started off quite euphoric. Then as it’s transpired that she’s under the control of the Revolutionary Guard again, and there’s no access, we’ve obviously got more worried.

“It’s possible it’s good news. It’s possible that it is a prelude to her release and getting treatment, and actually, all my fears are unfounded. And then it’s possible that something else is going on.”

Ratcliffe confirmed his father-in-law was prevented from seeing Zaghari-Ratcliffe on Tuesday. He said: “Her dad went down the hospital and tried to visit and spent a number of hours there, wasn’t able to get in. He took some lunch along, wasn’t able to deliver that and wasn’t able to phone her from the hospital reception.”

Zaghari-Ratcliffe was arrested at Imam Khomeini airport in Tehran in April 2016 while travelling with the couple’s daughter and accused of spying. The Thomson Reuters Foundation employee faced charges of spreading “propaganda against the regime”.

She vehemently denied the allegation, saying she was in Iran to visit her family, and her account was backed by her employer, but was sentenced to five years in jail in September of that year.

However, she was further imperilled when Boris Johnson, the then foreign secretary who is likely to become prime minister next week, mistakenly said she was “teaching people journalism” in Iran. While he later corrected his error, it was cited as evidence against her.

In 2016, a UN working group said it considered Zaghari-Ratcliffe to have been arbitrarily detained. Later Ratcliffe told Sky News he would be lobbying the new prime minister to take personal responsibility for the case.

He said: “We will be knocking on the door of whoever is the prime minister and saying this needs to be a prime minister-level issue.”