GPs are being urged to do more to spot signs of depression and anxiety to help millions of people who are currently undiagnosed.
At any one time, one in six adults suffers a common mental health condition such as depression, generalised anxiety disorder or obsessive compulsive disorder (OCD).
Other common conditions include panic disorder, social anxiety and post-traumatic stress disorder (PTSD), which is thought to be hugely under-diagnosed.
New guidance from the National Institute for Health and Clinical Excellence (Nice) aims to improve detection of the conditions.
Experts said there was not enough evidence to suggest screening the whole patient population but GPs should ask simple questions if they suspect somebody is struggling. Patients may also be asked if they are unable to stop or control worrying thoughts, possibly indicating an anxiety disorder.
GPs should also consider asking people who may have depression two questions: During the last month, have you often been bothered by feeling down, depressed or hopeless? During the last month, have you often been bothered by having little interest or pleasure in doing things? If the patient says 'yes', then the doctor is likely to ask further detailed questions.
Professor Tony Kendrick, chairman of the Nice guideline development group, said: "At present GPs have to consult several different disorder-specific guidelines when presented with patients with these problems, which makes it difficult to access the relevant information. This new guideline can be used by GPs as a handy guide to initial identification and referral, with quick reference points to the disorder-specific guidelines for details of treatment."
Paul Farmer, chief executive of mental health charity Mind, said: "Receiving a diagnosis and following this up with the right type of care can be key in determining whether someone progresses towards recovery or whether their mental health further deteriorates."
Care Services Minister Paul Burstow said: "The coalition Government is committed to improving the wellbeing of the nation. The aim of our mental health strategy, No health without mental health, being to prevent mental ill-health where possible, and to intervene early to avoid costly crisis.
"That is why we have input an additional £400 million for talking therapies for all. We welcome this Nice clinical guideline, which supports our goals."