Boris Johnson has raised Nazanin Zaghari-Ratcliffe’s case with Iran’s foreign minister during Brussels talks.
The foreign secretary is attending a summit to discuss the country’s nuclear deal after US President Donald Trump cast doubt on its future.
But Mr Johnson tweeted that he had also discussed “all our Iranian dual-national consular cases”.
Mrs Zaghari-Ratcliffe has been held in a Tehran prison for 21 months on spying charges she denies.
The mother-of-one was arrested in 2016 during a holiday visit to show her baby daughter Gabriella to her parents – but is now serving a five-year sentence.
Mr Johnson said he had also discussed the treatment of the BBC Persian service with the foreign minister, Mohammad Javad Zarif.
It is the second time Mr Johnson has met Mr Zarif in two months. The British foreign secretary travelled to Iran in December to press for the release Mrs Zaghari-Ratcliffe.
Mr Johnson had been criticised for comments he had made to a parliamentary committee in November. He told MPs that Mrs Zaghari-Ratcliffe had been training journalists in the country. He later later apologised for the comments.
Mrs Zaghari-Ratcliffe’s family had hoped that she could be released from her five-year sentence after an Iranian database listed her as eligible for release, but she remains in jail.
Up to 30 dual nationals from Britain and other western nations are understood to be detained in Iran, including British-Iranian Kamal Foroughi, who was arrested in 2011.
- 3 April 2016: Mrs Zaghari-Ratcliffe is detained at an Iranian airport while travelling home to London with her young daughter
- April-June 2016: According to Mr Ratcliffe, his wife was subject to “intense interrogation” for the first two months of her imprisonment and kept in solitary confinement
- September 2016: Mrs Zaghari-Ratcliffe is sentenced to five years in prison by Tehran’s Revolutionary Court
- January 2017: She loses an initial appeal against her sentence
- April 2017: Mrs Zaghari-Ratcliffe loses a final appeal in Iran’s supreme court to overturn her sentence
- December 2017: An Iranian database lists her as eligible for release
The Brussels summit was arranged to discuss the Iran nuclear deal, which since 2015 has seen Iran restrict its nuclear programme in exchange for sanctions relief.
French foreign minister Jean-Yves Le Drian, German counterpart Sigmar Gabriel and EU high representative for foreign affairs Federica Mogherini also attended.
After the meeting, Mr Johnson tweeted that European leaders were “unanimous” in the backing of the deal.