London's police force suspended an officer on Friday pending an investigation after video footage emerged of him kneeling on the side of a black suspect's head and neck.
"Some of the techniques used cause me great concern - they are not taught in police training," Metropolitan Police Deputy Commissioner Steve House said in a statement.
Reuters was not able to independently verify the video but Commissioner House said he was aware of a video showing part of the incident.
The Metropolitan Police referred the incident for investigation by Britain's independent police watchdog.
The suspect was arrested on suspicion of affray and possession of an offensive weapon, and remains in police custody.