British Transport Police have released two CCTV images of a man they would like to speak to in connection with incidents which saw women touched inappropriately.
They took place at Euston station and on board a Milton Keynes-bound train on September 23.
PC Dionne Lyon is investigating the two incidents.
She said: “The victim, a 56-year-old woman, was waiting for a train at Euston station around 9.15pm close to the departure boards when a man come up from behind and inappropriately touched her.
“He then tried to make a conversation with her, at which point she walked away towards a Milton Keynes-bound train. He followed her onto the train and began to stare at her during the journey, making her feel uncomfortable.
“He is also believed to have touched another woman during the train journey, before a train guard ejected him from the train at Hemel Hempstead for his behaviour.”
The appeal comes as BTP, Metropolitan Police Service Safer Transport Command, City of London Police and Transport for London work together as part of Project Guardian to create an environment on the transport network which does not tolerate intimidation and sexual harassment.
PC Lyon said: “Unwanted sexual behaviour of any kind is not tolerated anywhere on the rail network and we take all reports seriously.
“If you recognise the man pictured, I’d urge you to come forward and speak to officers investigating these incidents.
“I’d also urge for the second victim, who may have been touched by the man, to come forward so we can make sure she is OK and help to build a full picture of exactly what took place.”
Anyone with information can contact British Transport Police on 0800 40 50 40 or text 61016 quoting background number B5/LNA of 25/09/2013. Information can also be passed to the independent charity Crimestoppers, anonymously, on 0800 555 111.