British-Iranian Vahid Beheshti was on Thursday marking the 50th day of his hunger strike outside the British government's Foreign Office.
He is calling on the UK to act against Iran's powerful Islamic Revolutionary Guard Corps (IRGC) and to recognise them as a terrorist group.
Iran has been behind 15 credible threats to kill or abduct British citizens or UK-based people since last year, Security Minister Tom Tugendhat says.
The journalist and campaigner, who was twice detained by the IRGC in Iran, said he was outraged by the Iranian regime's attempts to silence critics in Britain.
He cited Iranian death threats towards people in the UK and the forced closure of the Iran International TV channel studio in London as the most pressing reasons behind his decision to go on hunger strike.
Some journalists in London have been given 24-hour police protection after receiving death threats.
Mr Beheshti and his wife Mattie Heaven marked their wedding anniversary on his 42nd day without food.
His daily diet of coffee, water and sugar cubes has caused his weight to plummet and his energy to wane.
By the anniversary he was noticeably thinner compared to the smiling groom in his wedding photos.
Mr Beheshti, who fled his homeland 24 years ago to set up a new life in Britain, said his wife understood the reasons for his hunger strike.
While his push for a proscription of the IRGC has yet to prove fruitful, Mr Beheshti said he had been encouraged by signals from UK Prime Minister Rishi Sunak’s government.
Foreign Secretary James Cleverly was told by MPs in the House of Commons in February that there had been a “major groundswell” in requests for the government to designate the IRGC a terrorist organisation.
Mr Cleverly said the IRGC's “malign impact” was felt across the region and the world but he stopped short of saying a ban was in the pipeline.
Iran’s execution of British-Iranian citizen Ali Reza Akbari on spying charges in January has further soured diplomatic relations with the UK.
