Police are probing the death of a 16-year-old taken ill at a rave in Hayes.
A spokesman for the Met police said they were called by the ambulance service at 4am on Saturday to reports of an unconscious man at an illegal rave on an industrial site in Pump Lane.
He added: “The 16-year-old boy was taken by London Ambulance Service to a west London hospital believed to be suffering from the effects of a drugs overdose.
"He was later transferred to a central London hospital where he died on Monday.
“A post-mortem examination will be held in due course."
The dead boy has been named as Daniel Spargo-Mabbs.