A man was left fighting for life after being stabbed at Harrow-on-the-Hill station on Saturday night.
Met Police officers and paramedics rushed to the scene, where they found the man outside the station at 11.30pm.
He was taken to hospital where he remains in a critical condition.
The Metropolitan Police said: "We’re working at scene of a stabbing at 11.30pm near #Harrow on the Hill station.
"A 26-year-old man has been taken to hospital, where his condition is critical."
However, they told The Evening Standard that the investigation is now being handled by the British Transport Police (BTP) as the incident occurred inside the station.
The area has been sealed off while forensic scientists examine the scene.
The BTP has been contacted for comment.
Anyone with information is urged to call 101 ref 8476/07dec or contact Crimestoppers.
