A hallucinogenic chemical found in magic mushrooms has successfully lifted severe depression in previously untreatable patients.

Scientists at Imperial College London induced intense psychedelic trips in 12 people using high doses of the banned substance psilocybin.

A week after the experience all the volunteers were depression-free, and three months later five still had no symptoms of the condition.

Published in the Lancet Psychiatry Journal, the study welcomes the results as "promising, but not completely compelling".

Its authors are now seeking further funding from the Medical Research Council and other bodies to carry out fuller trials.

They conceded, however, that the use of a placebo control, a crucial component of thorough clinical trials, would be difficult as it would be obvious who was having a hallucinogenic experience and who was not.

The psilocybin is believed to cause relief from depression by targeting receptors in the brain and disrupting the Default Mode Network, which is responsible for sense of self and is overactive in depressed people.