A man exposed himself to a female passenger before performing an "indecent act" in front of her on a south London train.

The woman was said to be left "extremely intimidated and upset" after witnessing the act on the Sutton to St Albans train.

Officers today released a CCTV image of the man they believe can help in the investigation of the reported incident on the Southern train service at around 2.40pm on December 17.

The man allegedly sat opposite the victim and performed the "disgusting actions" before exiting the train at Herne Hill.

PC Mark Luker said: “This was a revolting act that left the victim feeling extremely intimidated and upset. Nobody travelling on the railway should have to put up with these disgusting actions and we’re determined to find the man responsible.

“We believe the man seen on station CCTV can help us with our investigations. If you think you can name him, or if you have any information to help our enquiries, we’d urge anyone to get in touch.”

Anyone with information is asked to contact police on 0800 40 50 40 or text 61016, quoting reference SSUB/B2 of 18/1/16.