Five fire engines and around 35 firefighters tackled a fire at a derelict building on Troopers Drive in Romford.
Half of the first floor and roof of a two storey annexe were damaged by the fire. There were no reports of any injuries.
The Brigade was called at 2059 and the incident was over for firefighters at 2344. Crews from Harold Hill, Romford, Dagenham and surrounding fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.