Image caption The cause of Chronic fatigue syndrome is unknown.

Exercise and behavioural therapies are the most cost-effective and successful ways to treat Chronic fatigue syndrome, also known as ME, an analysis shows.

A study of 640 patients showed these treatments had the potential to save the economy millions of pounds if they were widely adopted.

The findings were published in the journal PLoS ONE.

However, another treatment favoured by patients' groups was shown to offer little value.

Nobody knows what causes the condition, yet a quarter of a million people in the UK are thought to have it.

The symptoms include severe tiredness, poor concentration and memory as well as muscle and joint pain and disturbed sleep.

There is now a strong case for the NHS to invest in providing these therapies Prof Paul McCrone, King's College London

An earlier version of this research, published last year, showed that cognitive behavioural therapy (changing how people think about their symptoms) and graded exercise therapy (gradually increasing the amount of exercise) were the most effective treatments.

However, the study provoked anger from many patients' groups which argued that pacing therapies (learning to live within limits) were both better and safer for patients.

Using data from the same set of patients, researchers compared improvements in levels of fatigue and activity with the cost to the NHS of providing the treatments.

It concluded that only cognitive behavioural therapy and graded exercise therapy could be considered cost-effective.

When the wider cost to society was considered, such as lost work or the cost of carers, those two therapies provided an overall saving.

Prof Paul McCrone, a health economist from King's College London, said: "There is now a strong case for the NHS to invest in providing these therapies."

Prof Michael Sharpe, from Oxford University, said: "This new evidence should encourage health service commissioners to provide these treatments to all those patients who need them."

Sir Peter Spencer, the chief executive of the charity Action for ME, said: "Patient choice should not be reduced as a result of this costing exercise.

"Action for ME will continue to recommend pacing as an effective treatment. We cannot ignore the number of patients who have been helped by it and the number of clinicians who find that it works for their patients."