A charity has called for people with major lung diseases to be retested after a study found that doctors may be misdiagnosing patients.

The British Lung Foundation (BLF) said anyone over 35 with asthma or chronic obstructive pulmonary disease (COPD) should be checked to ensure they have been diagnosed with the right condition.

A survey of 776 GPs for the charity revealed that 80% found differentiating between asthma and COPD "quite" or "very" challenging.

COPD is the umbrella term for a number of lung conditions, including chronic bronchitis and emphysema.

The study comes on the same day as the publication of a national audit that found COPD services often fall short of national standards and quality varies considerably across the NHS.

That research was carried out by the Royal College of Physicians, the British Thoracic Society and BLF.

COPD is the fifth-biggest killer in the UK, the second most common cause of emergency admission to hospital and one of the most costly in-patient conditions treated by the NHS, the report said.

According to the BLF, more than 3.7 million people are estimated to have COPD in the UK and more than five million have asthma.

It warned that misdiagnosis of the conditions could potentially affect millions of people throughout the UK.

In its survey, one in 10 GPs said they did not have appropriately trained staff to carry out or interpret spirometry testing, which measures how much air can be expelled from the lungs. Spirometry scores can usually be improved in patients with asthma, but this is not always the case in patients with COPD.

Less than one-quarter (24%) of GPs questioned were trained to carry out spirometry testing themselves.

Most people with asthma who receive proper treatment can lead normal lives.

COPD, in contrast, is a disease which gets progressively worse over time. The lungs become inflamed, leading to coughing and chronic breathlessness.

BLF chief executive Dame Helena Shovelton added: "Patients get understandably distressed and angry when they realise they have been misdiagnosed. We're calling for everyone over 35 with an asthma or COPD diagnosis to be re-tested and for this to be made part of the GP contract next year."