Richard Ratcliffe, the husband of the detained Iranian-British dual national Nazanin Zaghari-Ratcliffe, is to end his hunger strike after 21 days.
Mr Ratcliffe said he had told his wife he would end the protest on Saturday and that he would later be visiting hospital for a full check-up.
He told his supporters on the Free Nazanin Twitter account: "Today I have promised Nazanin to end the hunger strike. Gabriella needs two parents. Thank you all for your overwhelming care these past three weeks.
“The last act of the hunger strike will be our patchwork event in front of the Foreign Office at 13.30, then I will be going to the hospital for a full check-up. Thank you for keeping our family in the light.”
Mr Ratcliffe said his job was to "keep going", adding: "We probably hoped we'd get a breakthrough doing this. We haven't yet. I didn't want to go out in an ambulance. I want to walk out with my head held high." He also criticised Boris Johnson for his "telling" absence in talking to him during the protest.
His strike ended as a patchwork was due to be unveiled, made from all the patches that supporters have been sending throughout his time camped outside the UK foreign office.
Mr Ratcliffe began the demonstration outside the Foreign Office, in central London, last month and endured almost three weeks in his latest attempt to force action from the UK government to bring his wife home.
He was joined at a vigil on Friday by his seven-year-old daughter, Gabriella, and supporters, who gathered in a show of solidarity. But allies had started to raise concerns for his health and expressed fears that he could permanently damage himself.
Earlier on Saturday, the Labour MP Tulip Siddiq called for Johnson to visit her constituent "in solidarity". She tweeted: "It has been three weeks since Richard Ratcliffe last ate any food. In that time, not a single government minister has visited his camp outside the UK foreign office in solidarity.
“Will the prime minister take five minutes out of his day to visit my constituent today?”
Speaking on Thursday, Ratcliffe said: “I think there’s a basic medical limit on how long you do a hunger strike for. I made a promise to Nazanin, I made a promise to my family, Mum in particular, and to the family doctors, that I won’t take it too far.
“But yeah, I don’t think we walk away head held high feeling like it’s all been sorted.”
The Middle East minister, James Cleverly, met Mr Ratcliffe this week to discuss the current situation regarding his wife's detention in Iran, where she has been held since 2016 – more than 2,000 days.
After the meeting, Mr Ratcliffe said he had been left feeling “deflated”, adding: “If I’m honest, it felt like, you know, perfectly nice, sincere, caring, everyone in the room was caring. But you know we’re still stuck in the same status quo.
“We’re still stuck in the same problems that led us to end up on hunger strike.”
Throughout his protest, he has been calling for the British government to pay a £400 million debt to Tehran, dating back to the 1970s. The British debt is acknowledged as a precondition for the release of Zaghari-Ratcliffe, as well as other detainees. –Guardian