If, after three months there is no improvement, then the treatment should be discontinued.

The problem is doctors are told what to prescribe and then it's not funded

David Taylor, Maudsley Hospital

But chief pharmacist at the Maudsley, David Taylor says the system is not working.

The study revealed that less than half of health authorities provided funding for the drugs - Aricept, Exelon and Reminyl - yet nine out of ten specialists said they made them available to patients.

Where funding was provided it was usually limited; where it wasn't hospitals and GPs had to find the money themselves.

"This is a failing of the health authorities - the problem is doctors are told what to prescribe and then it's not funded," said Mr Taylor.

"It costs around �1,000 a year to put someone on these drugs. If they deteriorate so they have to go into a nursing home it can cost �1,000 a fortnight."

Better quality of life

The study also revealed a pattern of what the researchers have termed "NICE blight".

They believe that authorities are deliberately steering clear of drugs which are being looked at by the National Institute for Clinical Excellence, which is due to issue guidance on the use of Alzheimer's disease treatments by the end of the year.

Dr David Wilkinson, consultant in old age psychiatry at Moorgreen Hospital in Southampton also believes there is a system of "rationing by age" in operation.

"We care more about preserving a grade II listed building, built in 1925, than we do about the people who built it," he claimed.

There are an estimated 450,000 people with Alzheimer's disease in the UK and the Alzheimer's Disease Society believes that all who can benefit from the drugs should have them.

They drugs, known as cholinesterase inhibitors can have side effects including nausea and cramps and do not lead to any improvement in some patients.

But when they do work many sufferers and their carers say the drugs lead to a reduction in anxiety, improved memory and confidence and a better quality of life.

Anxiety can be reduced

A survey for the society earlier this year found that, of 1,000 people with Alzheimer's disease receiving the drugs, almost three quarters said symptoms stabilised or improved.

Both the Alzheimer's Disease Society and specialists are hopeful that this will iron out the inequalities in funding.

"With new clear guidelines we would expect that the system would have a better chance of working," said David Taylor.

Shadow Health Secretary Dr Liam Fox said: "Labour's prescribing policy of rationing on the basis of where the patient lives is a completely unacceptable way to run the health service.

"Tony Blair and Alan Milburn must put this right immediately. They need to begin by admitting that rationing goes on.

"They must then follow Conservative proposals designed to make sure that prescribing is undertaken on the basis of medical and scientific practice, not geography."