"Hopefully her transfer to hospital means that she is getting treatment and care, despite my distrust of just what pressures can happen behind closed doors. It is unnerving when we don't know what is going on," he said.
Zaghari-Ratcliffe, 40, was arrested in Iran while traveling with the couple's young daughter in April 2016 and has been sentenced to five years in prison after being accused of spying, which she and her family vehemently deny.
She and her husband recently ended a hunger strike designed to call attention to her plight. British officials have failed to secure her release despite repeated efforts. Her father said he visited the hospital in Tehran Tuesday but was not allowed to see his daughter, who has been out of contact with her family.
British officials urged Iranian officials to let her have immediate contact with her family and said her treatment has violated all international norms. Foreign Office minister Andrew Murrison told Parliament the government is worried Zaghari-Ratcliffe may face abuse and be forced to sign a bogus confession.
"We are concerned," he said. "I want to appeal to the better nature of people in Tehran to do what is right for Nazanin." He conceded, however, that Britain's options and influence are limited, even though Prime Minister Theresa May has raised it with Iran's leaders.
The Free Nazanin Campaign said in a statement that it does not know what treatment she is receiving or how long she is expected to remain in the hospital.