As a small boy in 1980, Omar saw his father, Amer, a prominent trade unionist and lawyer opposed to the dictatorship of Colonel Gaddafi, dragged from the family home in Tripoli by the Libyan secret police. He was subsequently executed.
About seven years later, the young Mr Deghayes and his family managed to secure exit visas, so Omar could receive treatment for an eye condition, and fled to Britain, hoping for a new life.
Today Mr Deghayes is one of eight British residents being held in Guantanamo Bay. During his three-and-a-half years' incarceration he has been tortured, held in solitary confinement for months, had his finger smashed, lost the sight in one eye and has resorted to a hunger strike, unable to defend himself in a court.
Omar's sister, Amani, said the family hoped their anguish had ended when they left Libya in 1987 and made a new home as refugees in Britain. Now, she is angrily pressing the Government of their adopted home to help bring her brother home. She said: "It is something everyone wants for themselves, to be able to feel you don't have to watch your back for no reason. If you have done something wrong, you want to think that you are going to get a chance to speak about it and say what you think and answer for yourself. It just seems that is not the case any more."
The first thing Omar's family knew about his incarceration was when his name appeared on an internet list of America's 50 most wanted terror suspects.
Mr Deghayes, now 35, was seized in Pakistan in January 2002 after being recognised as appearing on a Chechen training video seized by the Spanish government. His lawyer and family insist this is a classic example of mistaken identity.
On Thursday, lawyers for Mr Deghayes and two other British residents being held at the base won the first round of their legal battle to force the Government to press their case in Washington as international pressure grows for the notorious American base to be closed for good.
The case of Mr Deghayes highlights the plight of eight British residents who are still being held despite the fact that nine other British detainees have all been flown home and released without charge.
Yesterday, international pressure grew for an end to the Guantanamo Bay base where about 500 men have languished without trial for years.
The Government insists it cannot act on behalf of the men because they do not hold British passports, even though several have refugee status and some have British families and children waiting for them.
Kate Allen, UK director of Amnesty International, said: "Omar's current situation is the worst of all worlds. Not only is he trapped within Guantanamo's cruel and arbitrary system but the UK is essentially trying to wash its hands of him. As with other UK residents at Guantanamo, we need to see the Government making specific demands on the US authorities for either an early and properly fair trial for Omar, or his immediate release and safe return to Britain."
Omar and his family fled their homeland to Brighton and were granted political asylum. He grew up in Brighton and went to college to study to become a solicitor, hoping to follow in his father's footsteps. His mother, sister and brothers were all granted British citizenship but Omar's application was being considered when he went travelling four years ago before retaking his solicitors' exams in Huddersfield. He visited Malaysia and Pakistan before ending up in Afghanistan where he got married and had a son. The next his family heard, he had been arrested and has become one of eight British residents in legal limbo.
They describe him as a devout Muslim, who occasionally preached at a Brighton mosque but say he was no extremist and travelled to Afghanistan out of curiosity about the Taliban regime. They insist he has shown no support for terrorism.
At home, his sister cannot bring herself to read her brother's censored letters home. She said: "My brother's situation is quite shocking. The fact no officials are doing anything about it is even more shocking to me."
British residents at Camp Delta
* BENYAM MOHAMMED
Originally from Ethiopia, but lived in London since 1978 seeking asylum for several years. He travelled to Afghanistan in 2001 before fleeing to Pakistan after the American-led invasion. The 27-year-old is reported to have been held and tortured in Morocco before being taken to Kabul and then Guantanamo.
* SHAKER AAMER
A Saudi Arabian citizen who has lived in south-west London. Held since he was captured in Afghanistan in 2002. His wife of eight years, Zennira, and four children are British citizens. He applied for British nationality when he was seized in Pakistan. Alleged to have been tortured in Kabul, and became a spokesman for the detainees. His lawyer, Clive Stafford Smith, said he had a 43-inch feeding tube in his nose when he saw him last month.
* BISHER AL-RAWI
Fled to Britain from Iraq with his family 20 years ago. He was arrested in Gambia where he had travelled with Jamal el-Banna. He was accused of taking a weapon of mass destruction to Gambia. His lawyers say it was a battery charger.
* JAMAL EL-BANNA
Refugee from Jordan who lives in London with his wife and five children, all of them British. Arrested in Gambia with Bisher al-Rawi.
* AHMAD ERRACHIDI
A Moroccan who worked as a cook in London for 18 years. He was seized in Pakistan and is said to have been sold to US forces. He has been in solitary confinement for more than two years, and is accused of attending a terrorist training camp in July 2001. His lawyers have proof and witnesses showing that he was working in a London kitchen at the time.
* AHMED BEN BACHA
An Algerian who lived in Bournemouth. He was refused refugee status, but granted indefinite leave to remain. Lawyers are still attempting to gain access to him so they can press his case.
* ABDELNOUR SAMEUR
An Algerian from Harrow, north London, who was granted refugee status in 2000. British lawyers say they are still trying to gain access to him.Reuse content