A letter from the Prime Minister to the mother of Dr Abbas Khan has called the surgeon's death a "sickening and appalling tragedy" and says the Syrian regime must "answer for it".
Their despicable treatment of him and refusal to engage with us or the Czechs to enable us to support him is utterly unacceptable. We will continue to press for those responsible to be held to account.
The letter, dated December 20, finishes with a handwritten note saying: "You are in our thoughts and prayers".
A hand-written note at the bottom of the Prime Minister's letter to Mrs Fatima Khan says "You are in our thoughts and prayers".
The letter, dated December 20, calls Dr Khan's death a "sickening and appalling tragedy" and adds that "it is right that the Syrian regime should answer for it".
Dr Abbas Khan's sister, Sara, has told ITV News that she expects the British government to get answers from the Syrian regime. "This is the least they can do," she added.
The sister of the British surgeon Dr Abbas Khan who died in Syria said that the Prime Minister has sent the family letters.
Sara Khan told ITV News that David Cameron said "he is now going to help us get answers but nothing has actually been said as to how they expect to do this and when".
Scotland Yard is to be involved in the post-mortem process surrounding the death of British doctor Abbas Khan, the family's solicitor has said, after his body was flown back to the UK.
Nabeel Sheikh issued a statement which read:
The family are relieved that his body has been repatriated. Dr Khan is being transported by ambulance to the Coroner's Court in Walthamstow for the purposes of a post-mortem.
The Home Office is organising the process but, as a matter of course, Scotland Yard is actively involved given the circumstances surrounding Dr Khan's death are highly suspicious.
The family of British surgeon Abbas Khan have employed an independent pathologist to oversee the post mortem on his body following his death in a Damascus prison.
Nabeen Sheik, a lawyer for the family said the results of the post mortem were expected tomorrow.
The body of Dr Khan was returned to the UK today.
The mother of a British surgeon has demanded answers after accusing Syria of "killing" her son following his death in a Damascus prison.
The circumstances in which Dr Khan, a 32-year-old orthopaedic surgeon from London, died while in detention in Syria remains in dispute.
Speaking after his body arrived back in the UK Fatima Khan said: "I don't know why they killed my son and I want to ask why. Why on the release date they killed my son, I want answers. They are liars, every ministry is liars in Damascus."
British surgeon Abbas Khan's body is being flown to London this morning, just days after he was found dead in his cell. Syrian authorities have claimed that the surgeon from Streatham in South London took his own life, but his family insist he was murdered.
Mr Khan was arrested 48 hours after arriving in Syria last November.