A train was cancelled last night because someone urinated on the driver's seat, passengers were told.
Hundreds of commuters were left waiting on the platform after the mysterious discovery of a pool of liquid behind the locked door of the train's driver cab.
The driver is said to have announced to passengers that someone had urinated on his chair.
The 21.52 service had been scheduled to travel from London Victoria to London Bridge.
Passengers were due to start their journeys to Battersea Park, Clapham Junction, Wandsworth Common, Balham, Streatham Hill, West Norwood, Gipsy Hill, and Crystal Palace.
Stephen Hull, who was waiting for the train, tweeted: "My delayed train home cancelled cos somebody p****d in driver's seat.
"They took the entire train away cos the driver complained. Hundreds of people stuck at Victoria."
Mr Hull said he had seen a puddle of urine in the driver's cab.
Southern said they were investigating the incident but could not confirm that the suspect liquid was urine.
They said no member of the public could usually access the driver's cab and this was part of their investigation.
A spokesman for the train company said: "The 21.52 Victoria to London Bridge service was cancelled last night following reports from the driver that the driver’s seat was wet and unuseable.
"Passengers who were due to travel on the 21.52 service were able to complete their journey on the 22.22 service, and we apologise to them for the inconvenience this caused."