The Court of Appeal ruled that the National Institute for Health and Clinical Excellence (NICE) -- the body that controls the prescription of new drugs -- must be more transparent about how it calculates the cost-effectiveness of new treatments.

In a ruling delivered Thursday, the judges found the process by which NICE decided to restrict Alzheimer's drug Aricept to patients with a moderate version of the degenerative brain disease "was procedurally unfair".

They added that NICE should release a full version of the cost-effectiveness model used to produce guidance for the drugs.

NICE had decided in 2004 that the drugs, which cost about £2.50 a day and slow down the progress of the disease, are not cost-effective for patients in the early stages of Alzheimer's. This decision was upheld by a court in 2007.

Drug companies Eisai Ltd and Pfizer Ltd, which challenged the NICE decision, welcomed the Court of Appeal's ruling, saying it brought new hope for Alzheimer's patients.

Nick Burgin, managing director of Eisai, said: "We believe that this decision represents a victory for common sense. As soon as we have reviewed their cost-effectiveness calculations we will submit any new findings to NICE.

"We hope that this action will ultimately restore access to anti-dementia medicines for those patients at the mild stages of Alzheimer's disease."

NICE chief executive Andrew Dillon said: "We will be considering very carefully the findings and the implications for the time it takes us to provide advice to patients and the NHS on the use of new treatments.

"It is important to recognise that we have not been asked to amend or withdraw our current guidance on the use of these drugs to treat Alzheimer's disease: the drugs continue to be recommended only for people with moderate Alzheimer's disease."

Neil Hunt, chief executive of the Alzheimer's Society said: "Today's decision is a damning indictment of the fundamentally flawed process used by NICE to deny people with Alzheimer's disease access to drug treatments."

Alzheimer's disease is the most common form of dementia, affecting around 417,000 people in the UK.