The victim of a “frightening” sexual assault was grabbed by a pervert on the Northern line after a Saturday night out, police have revealed.

British Transport Police (BTP) released CCTV images this week of a man who officers are trying to identify, which happened in the early hours of Sunday, August 15.

The investigating officer, PC Mark Gilfrin, said: “A 20-year-old woman from south London was indecently assaulted by a man on a southbound train from Colliers Wood.

“The man grabbed her chest aggressively before getting off at South Wimbledon. This was a very frightening ordeal for the victim and I am determined to find the man responsible.”

Officers released CCTV images of a man they want to speak to, who is described as Asian, in his 20s, of large build and about 5ft 10in. He was travelling with two other Asian men.

If you recognise the man in the photos call 0800 40 50 40 and quote incident number 39 (August 15), or Crimestoppers anonymously on 0800 555 111.