This terrifying video shows the speed and ferocity with which flames from faulty Christmas tree lights can spread through a family home.

The video was tweeted by London Fire Brigade at a time when millions of people across the country are excitedly putting up the their festive decorations.

According to the tweet, the fire, which is caused by a set of faulty Christmas tree lights, spreads across the room in just 40 seconds.

It shows a real tree, which hasn’t been watered, placed in the corner of a room.

Zero seconds: All is well

At about five seconds into the video, flames can be seen deep within the tree, before quickly spreading upwards and filling the room with smoke.

12 seconds: Fire already licking the ceiling

Flames then pour over the ceiling and start destroying other furniture within the room.

20 seconds: The whole room is ablaze

The video is from the government’s Fire Kills campaign, an initiative to improve fire safety in the home.

In its tweet, LFB asks people to check their Christmas tree lights are in good condition before using them - and to switch them off at nights.

It also implores people to make sure they have working smoke alarms.

The tweet reads: “A house fire, most likely sparked by faulty Christmas tree lights, envelopes a living room in a shocking 40 seconds.

"Check your Christmas tree lights are in good condition & turn them off before you go to bed. Make sure you have working smoke alarms.”

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