An Eritrean asylum seeker who was due to be forcibly removed to France today under the “one in, one out” scheme has had his ticket cancelled after making a serious attempt on his life, the Guardian understands.

Other detainees said they believed he had made an attempt on his life because he feared he would be in danger in France due to his specific circumstances had he been forcibly returned there. He was discovered yesterday by his cellmate, who raised the alarm. He is now on round-the-clock suicide watch in detention.

Under the terms of a treaty agreed last August between the UK and France, one asylum seeker who arrives in the UK on a small boat from France is returned in exchange for a person who has not tried to cross the Channel. According to the Home Office, 605 people had been returned to France as of 28 April, and 581 had been brought to the UK. On 9 May, 196 people crossed the Channel in three boats.

Incidents of self-harm are not uncommon among detainees, and asylum seekers often have a history of trauma. With previous self-harm or suicide attempts among those due to be removed under “one in one out”, many have subsequently been deemed fit to fly. In one recent case, a man had self-harm scars all over his body and was bandaged up and put on a plane. Home Office officials said that after a medical assessment he had been deemed fit to fly.

One detainee, who witnessed the incident on Tuesday, said: “We think the man had been in detention for 17 or 18 days. When he found out he had been given a ticket for France he said he felt so emotionally tired after everything he had been through. We think that is why he tried to end his life. We feel so sorry about what happened to him. We are all in the same situation, but we don’t want to see anyone end their life over being sent to France.”

Emma Ginn, the director of the charity Medical Justice, which supports immigration detainees, said: “Of 20 of our clients detained for ‘one in, one out’ assessed by our independent clinicians, all 20 had clinical evidence of a history of torture, ill treatment and/or trafficking, and all 20 had serious mental health conditions.

“The news of what is understood to be another serious suicide attempt cannot come as a surprise to the Home Office. We and others have repeatedly warned that safeguards are so dysfunctional that more suicide attempts and even deaths could result.”

The Home Office has been approached for comment.

• In the UK and Ireland, Samaritans can be contacted on freephone 116 123. In the US, you can call or text the National Suicide Prevention Lifeline on 988, chat on 988lifeline.org, or text HOME to 741741 to connect with a crisis counselor. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at befrienders.org