Transport police have released CCTV images in the hunt for a man accused of sexual assault on an underground train in South London earlier this year.

The sexual attack took place on the Northern Line between Elephant and Castle and Balham tube stations on Monday, August 3, between 6am and 6.30am British Transport Police (BTP) said.

BTP said the man sat down next to the woman victim "without warning" and sexually assaulted her:

"The victim, who was seated on the service as it travelled between Elephant and Castle and Balham stations, was approached by a man.

"Without warning the man sat down and sexually assaulted her.

"He then pulled drugs from his pocket and offered them to the victim before asking her to get off the train with him to take the drugs.

"He also stated he was in possession of a knife," a spokesperson for BTP described.

They added that both the suspect and his victim left the train at Balham, and that she had noticed him walking near her after she left the underground.

"Officers believe the man in the CCTV image may have information which could help the investigation," the BTP spokesperson continued.

"If you recognise him, or have any information, please contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 2000051915.

"Alternatively, you can call Crimestoppers anonymously on 0800 555 111."