Police are appealing for help after a 22-year-old man was robbed by two men – claiming to have a knife.
The incident, on Thursday April 17, began on board the 10.52pm Faversham to London Victoria service.
Detective Constable Denis Mahoney, of British Transport Police (BTP)'s robbery squad, said: "The victim got on the train at Faversham station, Kent.
"At 11.15pm two men boarded the service at Gillingham station and sat next to him.
"One of the men said he had a knife and pressed an object up against the victim’s leg while the other man took property out of his bag.
"The victim tried to flee the train at Bromley South station, but the pair kept him there against his will.
"When the train reached London Victoria, they marched him to a cash point in the station and forced him to withdraw a large quantity of cash from an ATM.
"They then fled the scene with the money in the direction of Buckingham Palace Road."
BTP's robbery squad have been analysing CCTV footage from on the train and station and have released images of two men they think might have crucial information.
DC Mahoney added: "Thankfully robberies like this are incredibly rare on the railway network and the public can be assured we are doing all we can to catch those responsible and bring them to justice.
"This was understandably a very frightening ordeal for the victim and I would urge anyone who recognises the men pictured to get in touch, as I feel they may be able to greatly help the investigation."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference SSUB/B6 of 12/05/2014. Information can also be passed to Crimestoppers on 0800 555 111.