Plans for a national network of 250 psychological treatment centres to provide therapy for 1 million people a year are being considered by ministers to tackle a national epidemic of depression and anxiety.

A framework for making behavioural therapy freely available under the NHS will be set out today by Lord Layard, a Downing Street adviser who has convinced the prime minister that mental illness has become Britain's biggest social problem.

He will call for an extra 10,000 therapists to be trained over the next 10 years to provide an alternative to pills.