Eight fire engines and around 60 firefighters responded to a fire on a school grounds in Canons Park, Harrow.
A single story boiler house at the site was destroyed by fire. One of the Brigade's 32m ladders was sent to the scene as part of the response. There are no reports of any injuries.
The Brigade was called about the incident at 0142, and Control Officers mobilised crews from Stanmore, Mill Hill, Hendon and surrounding fire stations to the scene. Crews had the incident under control by 0358.
The cause of the fire is under investigation.