British Transport Police have renewed an appeal to help trace a man wanted in connection with a sexual assault.
The incidents happened on a Milton Keynes bound train on September 23.
CCTV images of the man investigators want to speak to have already been issued and they are urging anyone who recognises him to get in touch.
PC Dionne Lyon, said: “The image of the man in the CCTV is very clear. We are keen to speak to him in connection with the incidents, which took place on Monday, September 23.
“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 conversation with her, at which point she walked away towards a Milton Keynes-bound train.
“He followed her on to 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.”
Officers believe he boarded another train to Bletchley later that evening.
The appeal has been issued on the back of Project Guardian to create an environment on the transport network which does not tolerate intimidation and sexual harassment.
PC Lyon added: “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 is asked to 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.