Saturday marks 1,000 days since Nazanin Zaghari-Ratcliffe – who turned 40 in Evin jail, Iran on Boxing Day – was first detained in Iran.

When the West Hampstead mum and Thomson Reuters employee’s ordeal will end is unknown, but, marking Nazanin’s third Christmas in prison, husband Richard admitted there wasn’t the same – ultimately false – sense of momentum he felt last year.

He said: “We were here a year ago, we were here two years ago. Certainly last year we felt some strong momentum, and we felt sure it would be over quite soon.

“This year it’s a lot more circumspect. I’ve been a lot more reluctant to do interviews. There are only so many times I can say I am miserable without my family.

He told the Ham&High that he still hoped things could change in an instant: “I’m being very circumspect. We just have to see what happens, everything’s very high stakes.

“Of course we’ve thought about this milestone but I’m always thinking there’s a chance she might be home for Christmas, there’s a chance she might be home for her birthday, and we won’t get to this point.”

He also explained that support from the likes of Matthew Hedges – who was recently released from detention in the UAE – and his wife Daniela Tejada was invaluable.

He said: “It’s always really hard to know whose agenda to trust. All of the politicians, the journalists want certain things. With the families, we know we all want the same thing.”

Nazanin has been imprisoned by the Iranian Revolutionary Guard in the notorious Evin prison since being arrested in Tehran airport on April 3, 2016.

Richard and Nazanin’s daughter Gabriella, now four, has been in Iran in the care of her grandparents since then.

On her birthday, Amnesty International UK’s director reiterated the charity’s call for the British government to do more.

Kate Allen said: “[Nazanin’s birthday] is a yet another painful moment for Nazanin and her family.

“What should have been a day of celebration for Nazanin is once again a day of anguish – her third birthday behind bars. Despite everything, we send Nazanin our warmest wishes.

“Nazanin is a prisoner of conscience who should never have been jailed in the first place.”

Last week foreign secretary Jeremy Hunt said his staff were working incredibly hard on Nazanin’s case, and his “door was always open”.