Britain does have some cards in its favour.
They will talk about Yemen where Iran is backing the rebel Houthi forces.
Ever since the foreign secretary mistakenly told MPs that Mrs Zaghari-Ratcliffe was training journalists in Iran when in fact her family have always insisted she was on holiday, Mr Johnson has been under pressure to compensate for his error.
Mr Ratcliffe believes his wife is a pawn in a much larger diplomatic game, a bargaining chip whose life is being cruelly manipulated by some parts of the Iranian government to secure their political objectives.
The problem is that this debt has nothing to do with the Zaghari-Ratcliffe case.