A new study has cast further doubt on the idea that a virus called XMRV causes chronic fatigue syndrome.

US scientists linked the condition, also known as ME, to a mouse-like virus in 2009 after finding it in blood samples.

Now, UK experts say the discovery was a “false positive”, caused by cross contamination in the lab.

The illness may still be caused by a virus, they say, but not the one at the centre of recent controversy.

“Our conclusion is quite simple: XMRV is not the cause of chronic fatigue syndrome,” said Professor Greg Towers, a Wellcome Trust senior research fellow at University College, London, who led the research.

“It is vital to understand that we are not saying chronic fatigue syndrome does not have a virus cause – we cannot answer that yet – but we know it is not this virus causing it.”