Horne, serving 18 years for fire-bombing, today enters his 66th day of protest over the Government's refusal to set up a Royal Commission on vivisection, But while Horne's condition was still described as "serious but stable" a clinical review by doctors at York District Hospital decided that, contrary to reports by supporters of permanent liver damage, blindness, and loss of hearing, Horne had, in fact, "no irreversible conditions".
York Health Services NHS Trust had pressed for the transfer following increasing concern about the security threat to other patients from animal rights activists maintaining a vigil at the hospital.
The 10-mile journey to Full Sutton Prison, near York, got underway at 9pm and half an hour later Horne was relocated to the prison's medical centre, where he will be attended to by prison medical staff under the supervision of a consultant from the York hospital.
The hospital said that since Horne had refused permission to be fed or treated, he could be equally well cared for at the prison without any further disruption to the hospital's daily running.
Last weekend protesters sparked a security alert by climbing on the roofs of hospital buildings and tomorrow's planned opening of a cancer unit has been called off, on police advice, amid fears of clashes between activists and cancer research fund-raisers.
Police forces across Britain are still on alert in case Horne dies and his death sparks a wave of attacks by animal rights activists.
The Prison Service said: "Mr Horne's transfer follows a review of his condition by doctors at York District Hospital who decided, taking account of his refusal of food and medical treatment, there is no clinical need for him to remain in outside hospital. He continues to be offered medical treatment appropriate to his condition. Mr Horne has been refusing food since October 6 but has regularly taken some fluids."
Dr Peter Kennedy, chief executive of the Trust, said: "We carefully considered all the facts, including Mr Horne's medical condition, and came to the conclusion, after discussions with the prison authorities, that he could be safely returned to the prison medical centre.
"The Trust has an important responsibility to its 2,000 staff and 600 in-patients, as well as to hundreds of out-patients and visitors, to provide a safe and peaceful environment. This became impossible last weekend."
Horne's supporters said last night that they knew nothing about the move, which they described as "outrageous".
John Pounder, of the Animals Betrayed Coalition, said: "The man's on his death bed and they're just accelerating the process."