A "SLIP of the tongue" by Boris Johnson which has been used by Iran as justification to extend the jail term of a British woman was "not a serious gaffe", Cabinet colleague Liam Fox said.

Foreign Secretary Mr Johnson is expected to call his Iranian counterpart in an effort to defuse the row after he told MPs last week that Nazanin Zaghari-Ratcliffe was training journalists in Iran at the time of her arrest last year, something her employer and her family insist is incorrect.

Richard Ratcliffe, Ms Zaghari-Ratcliffe's husband said Mr Johnson should make a statement in Parliament to correct his mistake in an effort to prevent the sentence being lengthened.

International Trade Secretary Liam Fox said Mr Johnson would be "speaking to his opposite number to clarify" the situation.

He told BBC Radio 4's Today programme "we all make slips of the tongue", adding "we have got to be very careful that we are not overreacting to this".

On Sky News he said: "I don't believe that it is a serious gaffe.

"I think people in the Iranian regime, which is a very brutal regime, are using this as an excuse to hold a UK citizen in the most tenuous of circumstances.

"I think what we are seeing here is an attempt to discredit the Foreign Secretary without thinking first of all what the impact may be and what excuses it may give to the Iranian regime to act improperly."

Shadow foreign secretary Emily Thornberry said Mr Johnson should quit if his actions have damaged Ms Zaghari-Ratcliffe's prospects of freedom.

In a statement released by the Foreign Office, a spokesman did not offer any correction, saying instead that Mr Johnson's comments may have been "misrepresented" and they provide "no justifiable basis" for additional charges.

Ms Zaghari-Ratcliffe, who is serving a five-year sentence in an Iranian jail, was summoned to an unscheduled court hearing last weekend at which Mr Johnson's remarks were cited as proof that she had been engaged in "propaganda against the regime".

Reports suggest the new charge could add five years to her prison term, imposed over unspecified allegations of involvement in a supposed coup attempt against the Tehran regime, which she denies.

Mr Ratcliffe told the Today programme that a public retraction by Mr Johnson was required.

"I would like him to retract in Parliament, in Parliament rather than in a phone call to his counterpart, what he said, and say clearly that Nazanin wasn't training journalists and that she was just there on holiday."

He also called on Mr Johnson to visit Ms Zaghari-Ratcliffe in prison but insisted he remained hopeful his family could be reunited within weeks.

"I have promised Nazanin that it's still possible that they will be home for Christmas.

"I'm still battling on those terms."

Ms Zaghari-Ratcliffe insisted in her original trial that she was not working in Iran at the time of her arrest, but was visiting the country to show her infant daughter Gabriella to her grandparents.

Mr Johnson told a parliamentary committee on November 1: "When I look at what Nazanin Zaghari-Ratcliffe was doing, she was simply teaching people journalism, as I understand it.

"(Neither) Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed.

"And that I find extraordinary, incredible."

Following Saturday's hearing, the Iranian judiciary's High Council for Human Rights said: "His statement shows that Nazanin had visited the country for anything but a holiday.

"For months it was claimed that Nazanin is a British-Iranian charity worker who went to see her family when she was arrested ... Mr Johnson's statement has shed new light on the realities about Nazanin."

Ms Zaghari-Ratcliffe's employer, Thomson Reuters Foundation, urged Mr Johnson to correct his "serious mistake".