A police officer was under investigation today over claims he pushed a teenage boy through a shop window.
The 16-year-old was not seriously injured after the incident in Bromley, south east London, but was arrested for assaulting police.
The Independent Police Complaints Commission (IPCC) launched an inquiry after colleagues reported concerns to anti-corruption officers.
A spokeswoman said a member of the Metropolitan Police's territorial support group has been warned he is under investigation.
The alleged assault took place in Bromley High Street at about 11.30pm last Saturday.
Borough police officers were dealing with a disturbance on a bus involving a large group of youths.
A territorial support unit arrived in support, but the officers remained in the van while several suspects were questioned nearby.
Two young women approached the parked van and a pair of officers got out to speak to them.
At this point one of the officers "came into contact" with the 16-year-old and he crashed through the window of Magnet Kitchens.
The boy was arrested, taken to Bromley police station, interviewed and released on bail before being told no further action would be taken.
IPCC Commissioner Mike Franklin said colleagues are examining CCTV and appealed for witnesses to contact the watchdog.
He said: "We are particularly keen to speak to the two young women who approached the TSG (Territorial Support Group) van, as well as anybody else who witnessed the contact between the TSG officer and the youth who fell through the window, either from the street or perhaps as they passed by on the 208 bus."
A Metropolitan Police spokesman declined to comment.
Anybody with any information is asked to contact the IPCC on 0800 096 9070 or email Bromleyipcc.gsi.gov.