The Archbishop of Canterbury could broker the release of a British mother who is jailed in Iran and caught at the heart of a diplomatic row.

Nazanin Zaghari-Ratcliffe, 38, was arrested in Iran last April while on holiday according to her family and her employer the Thompson Reuters Foundation. But Foreign Secretary Boris Johnson told the foreign affairs select committee ten days ago that she was training journalists.

The comments have been cited by Iranian authorities as proof of her guilt and could lead to her five-year sentence being doubled under charges of fuelling 'propaganda against the regime'.

But Tom Tugendhat, Conservative MP for Tonbridge and Malling and chair of the influential foreign affairs select committee, suggested to Johnson on Monday that religious leaders be used to negotiate Zaghari-Ratcliffe's release with the Islamic clerics who run Iran's judicial system.

'This poor woman is being used as a political football not only sadly here but in Iran,' Tugendhat, who himself is a Catholic, told MPs in the Commons on Monday.

'Would he [Johnson} consider calling on people in our own system who could talk to the Mullahs, perhaps the Archbishop of Canterbury or indeed the Holy Father, to speak on behalf of this woman and seek to broker her release.'

The suggestion came during an urgent question from Labour's shadow foreign secretary Emily Thornberry who demanded Johnson apologise for his handling of the case.

Johnson again issued a qualified apology to the family and said: 'My remarks on the subject before the foreign affairs committee could and should have been clearer. And I acknowledge that the words that I used were open to being misinterpreted and I apologise to Mrs Zaghari-Ratcliffe and her family if I have inadvertently caused them any further anguish.'

Responding to the suggestion of the Pope or Welby's involvement Johnson simply said 'no stone will be left unturned' in efforts to secure her release.

Meanwhile the Prime Minister Theresa May is considering whether to invoke a 250-year-old legal principle to demand Zaghari-Ratcliffe's release. The move would see Zaghari-Ratcliffe being given diplomatic impunity status which would make her detention an act of aggression by Tehran against the British state, rather than against an individual. The option would raise the stakes in the case into a full diplomatic crisis and could make it harder for Iran to back down.

However officials in the foreign office are concerned Iran would refuse to recognise the principle, according to the Times, which has never been used before by the UK but has been by other countries including Germany.