The incident happened in Willesden High Road at about 1pm today (Saturday, 31 July) during a pre-planned operation to target the illegal use of e-scooters.
Officers had directed a male riding an e-scooter to stop but he failed to do so. The e-scooter then collided with a police officer, knocking him to the floor.
The police officer was treated at the scene before being taken to hospital, where he has been treated for a broken leg and concussion.
A 22-year-old man was arrested at the scene on suspicion of section 18 grievous bodily harm, assault on an emergency worker, obstructing a drugs search, failure to stop, dangerous driving, driving without a license or insurance, breaching the terms of a prison sentence and being unlawfully at large.
Inspector Martin Robbie, of North West BCU, said: “Officers put themselves in the face of danger on a daily basis and an incident like this demonstrates this.
“I would like to remind the public that the use of e-scooters, unless subject to a government approved scheme, is prohibited and use upon public highways and spaces will be subject to enforcement and potential seizure of the e-scooter.”