Young girls are again being warned to be on their guard against sexual assaults on south London buses as the hunt for the men responsible is stepped up.

Police have released CCTV footage of a second man they suspect of carrying out a series of attacks on girls aboard buses, most recently on a 15-year-old schoolgirl aboard the 131 bus.

The appeal comes weeks after an image of another man, wanted in connection of a series of attacks on the same 14-year-old girl, was featured on Crimewatch.

Superintendent Simon Ovens, of Merton police, described the suspect as a "threat to our youngsters".

The latest image shows a balding man in his 40s, of dark European appearance, and wearing a knitted cardigan, turquoise trousers, and yellow and green trainers.

He is pictured shortly after he assaulted the schoolgirl on September 27, between 8.20am and 8.30am, as it travelled down Worple Road on its way to Wimbledon.

The earlier image shows a man who attacked a 14-year-old schoolgirl when she travelled on buses between Wimbledon and Morden, first in October last year on the 163, then in December on the 163, then in June on the 93.

Several calls were made to Crimewatch after it was featured on the show last month, but unfortunately none of these have resulted in an identification.

DS Martin Groves said: "I was hopeful that someone would say that he is the guy who lives down my road, or works in that shop, but unfortunately the calls haven't panned out.

"Our chap doesn't seem to have featured since but there is an ongoing interest in the case."

Last autumn, young girls travelling alone on buses were urged to be on their guard after six young women were attacked on buses in and around Wimbledon in three months, many on the 57 and 163 routes.