The husband of Nazanin Zaghari-Ratcliffe, the British mother imprisoned in Iran, has called on Theresa May to intervene after the failure of efforts by Boris Johnson two years on from her arrest.

Speaking at an event in Hampstead to mark the second anniversary of her detention, Richard Ratcliffe said: “Nazanin is still in prison, so in simple terms, the Foreign Secretary has not done enough.

“The Prime Minister is more important, and just as we were pushing to meet the Foreign Secretary, at some point, if that is not enough, we have to push up another level and that’s the Prime Minister.”

Zaghari-Ratcliffe, a British-Iranian dual citizen, is serving a five-year prison sentence after being convicted of spying charges. She was arrested at Tehran Airport on 3 April 2016.

She denies the charges and maintains she was in Iran to introduce her young daughter Gabriella to her parents.

Ratcliffe added that he still wanted Johnson to be clear about the technicalities of what he thinks Zaghari-Ratcliffe’s rights are.

He said: “Before Christmas he vowed to leave no stone unturned, which was a political commitment, but legally, they say it is being treated as a consular case.

“Clearly this isn’t a consular case where the Government has no obligations.”

Ratcliffe was joined by over a dozen members of the local community including MP Tulip Siddiq in adorning a tree with yellow ribbons, from which they tied jokes and flowers.

The event was designed to lift the spirits of Nazanin’s friends and family, after what Ratcliffe called a “dark two years.”

Ratcliffe has not seen his wife or daughter, who is now three, since her arrest. Gabriella is being looked after by her grandparents in Tehran.

Zaghari-Ratcliffe is a dual citizen of Iran and the United Kingdom, but Iran does not recognise dual citizenship, making it complicated for the British Embassy to make contact.

“The last news I heard out of Iran is that the head of the prison had approved her release and it was in the hands of the Iranian foreign ministry to talk with the British Government,” said Ratcliffe.

Tulip Siddiq told the event: “Every time I table a question to ministers they always say that they can’t comment on the negotiations, so what I want to know is what are they negotiating and are they going to bring my constituent home?”

She added: “We had a meeting with Boris Johnson and he said he would leave no stone unturned, but we haven’t seen the results so I need to escalate this and have asked for a meeting with the Prime Minister.”

When asked if Johnson had been obstructive by denying her and Ratcliffe Information, Siddiq said: “I don’t know if it’s obstructive because he has no information to give because he’s done nothing on it. Perhaps he has no information to give because he hasn’t put it at the top of his priority list.”

In a press release earlier today, Ratcliffe said his wife’s detention had become a “test of endurance”.

“We didn’t expect to be needing to mark this anniversary – not after the hopes of Christmas and the Foreign Secretary’s word.

“But it remains a cold late Spring. Nazanin was told that if she wasn’t home by Christmas, at least it should be done by Nowruz (the Iranian New Year on March 20), and we should worry if we go past March 2018, with the storms that might lie ahead. And now we have.”

He added: “Our story has become a test of endurance, and there is a need to recharge spirits – particularly after the disappointment of the Foreign Secretary’s mission failing to deliver, and Nazanin becoming caught up in this government stand off – so we wanted the anniversary to be an occasion where we drew positive energy.

“That is what the outside can do, and we are grateful for people’s care.”

Siddiq said earlier today: “In November the Foreign Secretary promised to ‘leave no stone unturned’. But since his trip to Tehran, he has been missing in action.

“Nazanin does not have the luxury of time, and Boris Johnson must act before her situation gets worse.

“If he can’t deliver on this, then it is time that the Prime Minister stepped in.”

Ratcliffe said recent weeks have been a low point for his wife and she has suffered periodic panic attacks in her sleep.

The key question is whether Johnson has “given up on his promise to bring home Nazanin soon”, the Free Nazanin campaign said.

Ratcliffe and his supporters have requested to meet Johnson with lawyers present, to ask what are Nazanin’s rights in his view as the stand off continues.

On Tuesday a second event, ‘One Night of Freedom’, will be hosted by British Iranian comedian Shappi Khorasandi, with support from Amnesty and Redress.

Ahead of the event Khorasandi said: “What has happened to Nazanin could happen to me, to any Iranian-born Brit. The cruelty and injustice the Iranian government have inflicted on this family is unimaginable. I will not give up fighting for her release and for little Gabriella to be back with her mummy and daddy, where every three year old belongs.”

A Foreign Office spokeswoman said: “On the second anniversary of Nazanin’s arrest we continue to approach her case, and all of our British-Iranian consular cases, in a way that we judge is most likely to secure the outcome we all want.

“Therefore we will not be providing a running commentary on every twist and turn.”