The Appeal Court in London ruled yesterday that an NHS advisory body should have been more transparent in the way it made decisions over Alzheimer's drugs.

Judges said the National Institute for Health and Clinical Excellence (Nice) should have released details of how it reached its decision that the four drugs were not cost-effective.

The manufacturers of the drugs, which include Aricept, may now challenge Nice to review its guidance that the drugs be restricted to patients in the late stages of the disease.

The author Terry Pratchett is one of many Alzheimer's sufferers who currently pay privately for Aricept.

Any change of guidance by Nice is also likely to be adopted by the Scottish Medicines Consortium (SMC), which guides the NHS north of the border on the use of new medications.

Yesterday's Appeal Court ruling was welcomed by patient groups in England and Scotland, who have waged a long campaign to make the medicines available.

Jim Jackson, chief executive of Alzheimer Scotland, said: "It was grossly unfair of Nice to withhold the full details of their cost-effectiveness model.

"We will all now be able to examine how they reached their perverse recommendation not to prescribe these treatments at the beginning of the illness, when they are most likely to be of benefit."

Other products affected include Exelon from Novartis AG, Ebixa from Lundbeck A/S and Reminyl from Shire Plc, which is sold elsewhere as Razadyne by the firm Johnson & Johnson.

The judges said Nice had been acted wrongly in the run-up to its recommendation that the NHS should cease funding the £2.50-a-day drugs for early-stage patients because it failed to share details of its economic modelling.

Japan's Eisai Co Ltd, which markets the top-selling treatment Aricept with Pfizer Inc, had challenged the process, claiming it should have been able to see the detail of how that decision was reached.

Lord Justice Richards said withholding information put drugs companies at "a significant disadvantage" if they wanted to challenge a Nice ruling.

Eisai will now be able to assess Nice's cost-benefit analysis and any criticisms it has will have to be considered.

The SMC does not automatically follow the position of Nice. However, a spokesman said: "If the drug manufacturer finds problems with Nice's economic model and these problems are substantial enough for Nice to go back and alter its guidance, that change would be adopted in Scotland as well."