An anti-FGM campaigner from Gambia, who was diagnosed with terminal cancer and denied NHS treatment, has died.

The Guardian previously reported that the 54-year-old man known as Saloum, was denied free NHS medical treatment after he collapsed in the street last December. He died on Sunday evening after being rushed to Royal Derby hospital hours earlier.

Friends who were with him when he died said that even in the final moments of his life he was fearful that he might once again be sent away from the hospital because he was unable to pay for his NHS treatment.

Saloum fled Gambia a decade ago after falling foul of his government for condemning the widespread practice of female genital mutilation in his country. Three-quarters of Gambian women and girls aged 15 to 49 have undergone FGM.

After his collapse in the street it emerged that on arrival in the UK he was subjected to labour exploitation. The Home Office was alerted and sent him a letter on 25 February this year stating: “There are reasonable grounds to believe that you have been a victim of modern slavery.”

After Saloum’s collapse in the street last December he was diagnosed with two brain tumours and lung cancer and was told he did not have much longer to live.

Following initial treatment he was sent away because he was not eligible for free NHS care as an undocumented migrant. After pressure from the charity Doctors of the World, which argued that treatment for his cancer was urgent and immediately necessary, he was subsequently given some treatment at the hospital.

Saloum became homeless following his collapse in the street – he was previously accommodated in a place he said was unfit for human habitation by the man who subjected him to labour exploitation. His friends raised money for a bedsit for him and looked after him in shifts.

“Sal had been very distressed when he was sent away from the hospital after his initial diagnosis because he could not pay for his cancer treatment,” said one friend, who was with Saloum on Sunday night when he died.

“Last night, just before he died he became panicked and anxious and I could see he was scared he might be discharged again because he could not pay for his treatment. I knew him for a long time. He was a very brave soul the way he challenged FGM in Gambia. He had a very tough time in the UK because of the labour exploitation and never really had any time to enjoy his life.”

After the initial treatment Saloum received a bill from University Hospitals of Derby and Burton NHS foundation trust for £8,397, which he was unable to pay.

The letter stated: “Please be aware that should you require further treatment you will need to pay for this upfront and any care that is not immediately necessary or clinically urgent could be denied.”

The Doctors of the World’s director of programmes, Lucy Jones, said: “Sal was let down by the system at every stage and Doctors of the World supported him with over 20 hours of casework to make sure he got the care he needed. Sal should never have been refused help but the current policy meant hospital doctors and the GP didn’t know what to do and were unable to get clarity from the NHS leaving him without any care.

“Unfortunately Sal’s case was not isolated; the charging system is distracting medical staff from being able to deliver essential care and causing real harm to patients.”

A spokesman for University Hospitals of Derby and Burton NHS foundation trust said: “We are unable to comment on the care of individual patients due to patient confidentiality.”