Eight fire engines and around 60 firefighters were called to a house fire on London Road in Stanmore.
The roof and most of the first floor at a two-storey detached house were destroyed by fire. Thankfully, no injuries are reported.
The property had smoke alarms fitted but they did not activate.
A London Fire Brigade spokesperson said: “This incident is a reminder of just how important it is to have working smoke alarms in your home.
“Smoke alarms give the earliest possible warning when a fire starts. We encourage everyone to have smoke alarms fitted in every room where a fire could start, plus a heat alarm in the kitchen. It’s important to test them regularly.”
The Brigade's 999 Control officers received the first of ten calls at 1911 and mobilised fire crews from Stanmore, Mill Hill, Harrow, Hendon, Wembley fire stations plus firefighters from Hertfordshire Fire and Rescue. The fire was over by 2201.
The cause of the fire is under investigation.