Depression could be treated using anti-inflammatory drugs, scientists now believe, after determining that it is a physical illness caused by a faulty immune system.

Around one in 13 people in Britain suffers from anxiety or depression and last year the NHS issued 64.7 million prescriptions for antidepressants, double the amount given out a decade ago.

Current treatment is largely centred around restoring mood-boosting chemicals in the brain, such as serotonin, but experts now think an overactive immune system triggers inflammation throughout the entire body, sparking feelings of hopelessness, unhappiness and fatigue.

It may be a symptom of the immune system failing to switch off after a trauma or illness, and is a similar to the low mood people often experience when they are fighting a virus, like flu.

A raft of recent papers, and unexpected results from clinical trials, have shown that treating inflammation seems to alleviate depression.