An explosion ripped through a family home in a giant inferno after it was deliberately set alight.

Six fire crews spent four hours battling the blaze as it engulfed the terraced house in Huddleston Crescent, Merstham.

Luckily nobody was home at the time of the blaze – but police and fire services were quick to label the incident as arson.

Onlooker Donald Thompson, 50, was alerted to the fire after he heard a huge explosion just after 10pm on Sunday evening.

He said: "I heard a huge bang and the whole street ran out to look.

"The place looked beyond help. The flames were blazing out of the window.

"This is a terrible thing to have happened. What if the owner had been in? This could have been fatal."

Firefighters frantically fought the flames, and were able to stop it spreading to other houses.

Neighbour Emily Finch, 26, watched the drama from her bedroom window.

She said: "I had already gone to bed when I heard the explosion. It was mad.

"I looked out the window and the entire house had burst into flames.

"The fire quickly travelled up the stairs and then the whole roof went. I was gobsmacked. What if the owner had been in?"

Police are now appealing for anyone who might have seen something suspicious to come forward.

Neighbourhood inspector Charlotte Rimmer said: "Thankfully, no-one was in the house at the time of the fire, but it could have been very different."

Emergency services have been called to the street several times in the past six months, following a flurry of hoax 999 calls.

Mr Thompson said: "I've lost count of the amount of times we've had armed police or the fire brigade come out because of hoax calls.

"But what happened here today is a much more serious matter. Somebody must have a really evil streak in them."

Anyone with any information should call detective inspector Tony Giles at Reigate CID on 0845 125 2222 quoting reference RB/10/722.

A 22-year-old man from Tadworth has been arrested in connection with the fire and been released on bail until Friday, March 26, pending further enquiries.