Police broke up a cannabis factory in north Watford today after residents spotted a house with no snow on its roof.

Officers were alerted late last night after a resident reported a terrace house in Cromer Road was not covered in snow, unlike every other house in the street, and looked “extremely odd”.

Early this morning, at about 9.30am, police arrived at the three-bedroom property, which had a lot of condensation on its windows.

They then forced their way into the house. Inside, they found two rooms downstairs and all three bedrooms filled with plants of mixed maturity, lighting and power equipment and fertiliser.

An area was also being used to dry the plants after they were cultivated. Nobody was found inside the house.

In total, officers found between 150 and 180 plants, which would have a street value of £100 to £150 each. Some of the plants were one foot tall, while others were more than double in size.

However, it is not known how long the factory has been operating for or how many crops may have already been cultivated.

Inspector Matt Dillon, from the Watford and Rickmansworth intervention team, said: “After we received the information last night, we acted immediately and went to the address this morning. There was a lot of condensation on the windows and no snow on the roof.

“All the blinds were drawn and speaking to local residents, they identified very limited foot traffic one hour every week coming to the house to water and maintain the plants.

“There was a very strong smell in the street. The plants were in every single room and they had large fans. It was quite a professional set-up. There were vents at the rear of the premises so the smell was coming round and drew everybody's attention to it.”

Inspector Dillon said officers acted quickly and robustly to close the cannabis operation.

Forensics experts visited the scene earlier today before officers spent several hours emptying the house.

“These factories have got to be dealt with quickly,” he said. “We were concerned as it is a fire risk. And when they are not manned by anybody, it's a safety issue. We also wanted to send out a bit of a message.

“This was a very tidy, very neat, very well kept. Everything was laid out. It was a decent operation.

“Previously when someone's manned the property, there's been a bed, chair, magazines or DVDs. There was nothing like this here. They purely visited to cultivate and water it.”