A 40-year-old has been arrested on suspicion of making indecent images after a member of the public stepped in to stop a man from photographing children at Waterloo.
Police were called to the station yesterday morning to reports of a "fight" between two men.
Scotland Yard said a member of the public was apparently trying to detain a man he believed was taking pictures of schoolchildren.
"A 40-year-old man from Wandsworth was arrested at the scene on suspicion of making indecent images," said a spokeswoman.
"He was taken to a south London police station where he was later released on police bail to return on a date in late July pending further enquiries."
British Transport Police first attended the incident, just outside the station, shortly after 8am on Monday - but have since passed the case on to Lambeth borough police to investigate.
