GPs should have better access to psychological therapies to reduce the cost of extra physical healthcare caused by mental illness.

A report published by the London School of Economics shows only a quarter of all patients with mental illness receive treatment for their condition.

It is claimed while mental illness accounts for 23% of the total burden of disease, it only receives 13% of NHS health expenditure.

Leading the study, Lord Layard of the Mental Health Policy Group, blasted current NHS commissioners for failing to commission the mental health services NICE recommend.

He claimed more expenditure on the most common mental disorders would "almost certainly cost the NHS nothing".

"Altogether the extra physical healthcare caused by mental illness now costs the NHS at least £10bn," he said.

"Much of this money would be better spent on psychological therapies for those people who have mental health problems on top of their physical problems."

The report says the resulting savings on NHS physical care outweigh the cost of the psychological therapy, partly because recovery rates are high.

Professor Clare Gerada, Chair of the Royal College of GPs, said GPs face "tremendous challenges" in caring for patients with mental health problems in primary care.

She said improving access to talking therapies would be a "major step forward" for patients and GPS alike.

"GPs must have access to a range of talking therapies, from counselling and cognitive behavioural therapy to longer term psychotherapies, for the wide range of conditions that we see in our consulting rooms," said Dr Gerada.

The report has called upon the government to do more to ensure commissioners are using the £400m set aside for 2011-14 for the national roll-out of Improved Access to Psychological Therapy (IAPT).