A teenager was assaulted by a group of men as he walked through an underpass on Monday.
The 17-year-old was walking towards Shenley Church End and, as he approached the underpass at 12.21am, was pushed and hit his head on the brick wall, before he was assaulted.
He managed to get away uninjured but his wallet, containing a small amount of cash, bank cards and a student id card was stolen. The offenders were all white.
The first is around 18 years old, 6ft and well built wearing a white hooded top and black tracksuit bottoms. He rode a black BMX bike.
The second is also around 18, 5ft 10ins, well built, with short dark hair wearing a black T-shirt and grey tracksuit bottoms. No descriptions of the other two men are available.
Witnesses can call police on 101.