An ordinary-looking home in Merseyside was identified as a cannabis farm when police officers spotted hundreds of pigeons huddling together to keep warm on the roof. The house, just yards away from Newton-le-Willows police station attracted up to 300 birds because of the powerful lights and heaters needed to grow the plant.

Officers from the nearby police station became suspicious after the roof showed no frost in the bitter cold temperatures and executed a search warrant at the address where they found 14 plants capable of producing £1,200 ($1,800, €1,650) worth of the drug every three months. No one at the address was arrested and after the removal of the lights, heaters and other equipment, the birds flew away.

Police around the UK have been known to use heat detectors to spot possible homes which are growing the illicit herb. Penalties for cultivation of the plant in result in up to 10 years in prison.

"Police became suspicious on the first frosty morning of the winter about 10 days ago," an anonymous source told the Daily Star. "The roof was covered with about 300 pigeons all keeping warm....they've moved on now though."

In February this year Dutch police unearthed an "industrial scale" drug den after snow settled on every other roof on a street apart from one. After swooping on the address the police sent a tweet as a warning to any other prospective growers.

On 26 November, police in Manchester discovered a major cannabis farm containing about 400 plants in the city centre. Criminals were found to have been growing the Class B drug in almost plain sight out of a derelict building opposite the Crowne Plaza hotel, located in a busy part of the city.

Today (14 December) police seized cannabis plants, with an estimated potential street value of up to £170,000, in West Dunbartonshire, Scotland. Hundreds of the cannabis plants were found growing in a disused building on Dumbarton Road in Clydebank.