It means Britain no longer regards her case as simply a consular matter and raises it to the level of a legal dispute between Britain and Iran. The move was rejected as a violation of international law by Iran's ambassador to Britain, who said his country does not regard Zaghari-Ratcliffe as British.
Zaghari-Ratcliffe was arrested in April 2016 on charges of plotting against the Iranian government. Her family denies the allegations. Her husband Richard Ratcliffe welcomed the move Friday, saying it could lead to a resolution of her case within months.
"It changes the status for Nazanin's case," Ratcliffe told BBC radio. "Now it's also the British government's case and all the injustices that happen to Nazanin are effectively injustices against the British government."
He said the top priority is to have a doctor see Zaghari-Ratcliffe to provide urgent medical care. "A couple of months ago she went on hunger strike because she wasn't getting any treatment, and was promised it but it didn't happen, so she got very low again recently. I'm sure this will give her a big lift," he said.
Foreign Secretary Jeremy Hunt said legal proceedings against Zaghari-Ratcliffe in Iran were deficient and that she has been denied proper access to health professionals. "It's not a magic wand, it's not going to solve things overnight but it does create a different legal and political context," Hunt said of Britain's decision to offer diplomatic protection.
The British government has long been seeking her release without success. Hamid Baeidinejad, Iran's ambassador to Britain, said in a tweet Friday that the British government's move violates international law.
He said governments can only extend such protection to their own nationals and that Iran does not recognize dual nationality. "Ms Zaghari thus remains Iranian," he said.