Richard Ratcliffe emerged from a 40-minute meeting with Boris Johnson in Downing Street admitting there had been no breakthrough in his efforts to persuade the government to do more to secure the release of his wife from a Tehran jail.

Nazanin Zaghari-Ratcliffe was sentenced to five years for espionage in 2016, and Ratcliffe has been battling for ministers to make her case a higher priority.

It was the first meeting between the two men since Johnson became prime minister. Their relationship has been rocky ever since Johnson, while foreign secretary, mistakenly indicated that Zaghari-Ratcliffe had been in Tehran to train journalists.

The foreign secretary, Dominic Raab, and Ministry of Defence officials were also present at the meeting, and Ratcliffe brought his daughter Gabriella, five, and his mother.

Ratcliffe said Johnson had been warm and had assured him that the government was doing everything it could but that “it’s just complicated”.

Ratcliffe said: “I don’t stand here hopeful, if I’m honest. I stand here with my wife still in prison and things aren’t moving.”

He called for progress in a long-running legal dispute between the UK and Iran over a deal for Chieftain tanks struck before the Iranian revolution in 1979. An appeal court hearing is under way on whether the UK is obliged to pay interest on the sum it owes for the period since the Iranian ministry of defence was put under sanctions in 2008.

Ratcliffe said ministers insisted at the meeting they were looking at novel options to pay the debt that might get round the international sanctions, but he was told there were issues of moral hazard.

Diplomatic sources have said the British and Iranian governments have been exploring whether it is possible to pay the debt in the form of humanitarian aid. But Ratcliffe’s team came away with the impression that Johnson was not fully briefed on the issue.

“We obviously talked about the fact that there is a court case happening somewhere else in London at the moment and we’ve been linked to it,” Ratcliffe said. “I think it’s important there is progress on that and there’s progress in the way that everyone feels is lawful and following proper process.”

He urged the UK not to combine its talks with Tehran about the debt with a tough approach on hostage-taking. He said the government had to impose clear red lines or else there was a risk of other British-Iranian dual nationals being picked up by Iranian hardliners in the Iranian Revolutionary Guards Corps.

“Nazanin is being held by Tehran and used as a chess piece,” he said. “That wasn’t disputed in there, whatever the terminology. The UK obviously is wary of that tightrope it is walking between the US and Europe in Iran relations and the JCPOA (Joint Comprehensive Plan of Action nuclear deal ) and the dispute mechanism and so on.

“I was saying ‘I think this is different’. This is a global norm, that actually we all uphold universal values where hostage-taking shouldn’t be happening.”

Ratcliffe is expected to hold further talks with the foreign secretary and they are likely to discuss the option of UK sanctions on individual IRGC commanders once Britain has left the EU. Ratcliffe has been repeatedly told by British diplomats that they are determined to do nothing that could strengthen Iranian hardliners.

He said that the recent killing of the Iranian general Qassem Suleimani was terrifying for his wife. The fact that protests in Tehran over Iran’s handling of the mistaken downing of a Ukrainian airliner in Tehran had been blamed on the British ambassador Rob Macaire had made him very concerned about the possibility of a new wave of arrests of British nationals.

Ratcliffe said he did not discuss the prime minister’s previous errors, explaining: “We did not talk about the past.”

Asked about how his daughter reacted to going to Downing Street, he said: “It’s a surreal experience for a five-year-old. Sometimes you can protect children and sometimes you cannot. She declined the prime minister’s offer of apple juice and saw a cat called Larry. Sometimes she got a little bored and did some colouring.”