A safe and widely-used arthritis drug stops Alzheimer’s in its tracks, a British study has found.

The 20 men and women who were given Etanercept did not descend further into the disease – unlike those who were given a dummy treatment. Memory, mood and the ability to carry out vital everyday tasks such as washing and dressing were all, on average, stopped from getting worse.

The results, revealed at a major Alzheimer’s conference and dubbed ‘quite amazing’, are comparable with those for Aricept, one of the few existing Alzheimer’s treatments.

However, Aricept and other drugs do not work for everyone and their effects wear off relatively quickly.

With Alzheimer’s and other forms of dementia affecting more than 800,000 Britons and the number predicted to double in a generation as the population ages, David Cameron has described dementia as ‘the key health challenge of this generation’.

A drug already used for something else would be cheaper and quicker to test and get to patients.

Dr Doug Brown, director of research and development at the Alzheimer’s Society, said: ‘There is a desperate unmet need for new drugs for dementia but we know that getting treatments to market from scratch can cost billions and take decades.

‘Repurposing existing drugs could see new treatments for dementia available in a fraction of the time and at a fraction of the cost, so it is an opportunity we can’t afford to waste.’

The study by Professor Clive Holmes, a psychiatrist and Alzheimer’s researcher, focuses on a blood protein called TNFα, which is key to the pain, inflammation and destruction of the joints in rheumatoid arthritis.

It is also thought to trigger the death of brain cells in Alzheimer’s – and patients with more of it in their blood do worse than those with low levels.

Etanercept, which is injected into the stomach or thigh, stops TNFα from causing damage.

And given as a weekly jab for six months, it held Alzheimer’s at bay for that time, the Alzheimer’s Association International Conference in Copenhagen heard.

Professor Holmes cautioned that only a small number of patients were treated – but described the results as ‘quite amazing’.

He said: ‘Our results are better than we expected.

‘It is the first drug in a long time that has shown such promise.’

The professor is now seeking funding for a larger trial.

Many promising Alzheimer’s drugs fail when tested on hundreds and thousands of people (PLEASE KEEP) but if the drug fulfils its early promise, it could be given to dementia patients in as little as five years.

So far it has only been given to Alzheimer’s patients for six months. But it is hoped that given for longer, it would stall the disease for longer.

It may even prevent someone with slight memory lapses ever going to suffer full-blown Alzheimer’s.

Professor Holmes said: ‘We are not reversing the disease but we may be holding it back, so the earlier we start it the better.’

However, he stressed that much more research is needed.

Dr Eric Karran, of Alzheimer’s Research UK, described the results as ‘encouraging’ but cautioned: ‘We know that clinical trials have a high failure rate and so we need to see Etanercept tested further in larger and longer trials in Alzheimer’s disease.’

The jab costs around £180 a week. However, it is hoped that by the time it is cleared for use in Alzheimer’s, the price will have fallen. It may also be available in pill form by then.