A teenager was able to rape and assualt a six-year-old boy, despite being under the supervision of youth and social workers following an arson conviction.

The 15-year-old, who was jailed for five years at Oxford Crown Court on Tuesday for the rape and attack on August 5, was on a nine-month supervision order imposed by Oxford magistrates when the incident happened.

Police have said they have serious concerns about the quality of the care the teenager was receiving under the order. Det Sgt Ian Richings, the Oxford CID officer who led the rape investigation, said the teenager roamed free across the city, between three family addresses.

But social services and the youth offending team claim he was adequately looked after, and that they did not have a 24-hour duty of care.

The supervision order was imposed in March last year for an arson attack committed at an Oxford hostel where he was living. The teenager had previously been put on another nine-month supervision order for battery of an eight-year-old boy in September 1999. In that incident, the boy was taken to toilets in Bury Knowle Park, Headington, by the then 13-year-old, where his trousers were pulled down and his legs tied.

Det Sgt Richings said: "I had some major reservations about social services and their treatment. He was just roaming. He mooched between the three addresses, was constantly on the move and there was very little control over him."

He added there was a well-documented link between arson and sexual assault crimes, with offenders who committed one often also committing the other.

Social services spokesman Mike Biddulph said: "This boy was legally defined as a child in need, so social services were involved in supporting him and his family over quite a long period.

"He has had anger management training, and he and his family have had a huge amount of support."

Mr Biddulph added social services did not have a 24-hour duty of care for the boy, who still lived with his family. Addressing his criminal behaviour was dealt with by the youth offending team (YOT).

YOT spokesman Mike Simm said: "There was a requirement for at least weekly contact and there are sanctions that follow as a result of not keeping that contact.

"You have to have a supervision plan, which as it was focused on arson, involved working with someone from Oxfordshire Fire Service.

"I am confident that we fulfilled our responsibility in terms of that order."