A 17-year-old boy suffered a fractured eye socket after he was set upon by a gang in full view of town centre shoppers.
The boy was in the Subway takeaway in Cambridge Street between 3.15pm and 3.30pm on Sunday afternoon when he became involved in an argument with another teenager.
This teen was joined by a gang of boys outside the takeaway and attacked the victim both inside and outside Subway.
Police say between 10 and 15 people, mostly Asian teenagers, were involved.
The gang then followed the victim and his friend to Market Square and to an alleyway next to Wagamama’s in Exchange Street before the victim was again assaulted by one of the boys.
He suffered a fractured eye socket and bruising and was taken to Stoke Mandeville Hospital for treatment.
The offender is Asian, between 15 and 16 and 5ft 5ins and was wearing a grey hooded top and blue jeans.
Anyone with information about the incident is asked to contact the police enquiry centre on 101 or Crimestoppers anonymously on 0800 555 111.