Archie Battersbee is to have his life-support treatment turned off at 11am on Wednesday, his family has said.
It comes after Archie's parents, Hollie Dance and Paul Battersbee lost a Supreme Court bid to delay the withdrawal of his life-sustaining treatment pending a review of his case by a UN committee.
The 12-year-old has been in a coma since he was found unconscious by his mum in April and is currently being kept alive by a combination of medical interventions, including ventilation and drug treatments, at the Royal London Hospital in Whitechapel, east London.
His parents were granted a Court of Appeal hearing on Monday after the Government asked judges to urgently consider a request from a UN committee to keep treating Archie while it reviews his case.
Archie Battersbee
Hollie Dance
Archie's mum, Hollie Dance
Yui Mok
But after considering the matter, three judges refused to postpone the withdrawal of life-sustaining treatment beyond midday on Tuesday.
They also refused to grant permission to appeal against their ruling at the Supreme Court.
Ms Dance said in a statement: “Heartbreakingly, the hospital trust have told us this evening that we cannot move Archie to a hospice.
“We want to make an urgent application to the European Court of Human Rights, but the trust are saying that that has to be submitted at 9am, which gives us and our lawyers no time to prepare it.
“They also demand to see a copy of it, which they have no right to see. However if this does not happen, they say they will withdraw treatment tomorrow morning at 11am. This is cruel and we are absolutely appalled.”
Speaking after the ruling on Tuesday, Ms Dance said that Archie had been “let down” by the legal system.
Asked for her reaction to the decision, the 12-year-old's mum said: “Very disappointed in the system, very let down, very disappointed.
“I can honestly say that Archie would be very, very disappointed in our justice systems.
“This is somebody’s child … they’re not just taking a child away from me and Paul, they’re destroying the whole family.
“It’s not right, it’s not right, and something needs to be done – reform desperately needs to be taking place in this country.”
The hospital where Archie is being treated said earlier it will work with his family to prepare the withdrawal of his life-sustaining treatment following the Supreme Court ruling.
Alistair Chesser, chief medical officer for Barts Health NHS Trust, said: “Our deepest sympathies remain with Archie’s family.
“As directed by the courts, we will now work with the family to prepare for the withdrawal of treatment. We aim to provide the best possible support to everyone at this difficult time.”