Landlords are being urged by police to be on the lookout for cannabis factories.

This morning the Oxford Mail reported 26 cannabis factories have been discovered in the county so far this year. Now police are warning landlords who let their houses out to report anything suspicious.

In the whole of the Thames Valley Police region this year there have been 123 cannabis factories found compared to just 42 last year.

Acting Assistant Chief Constable George Wilson said: "Following the reclassification of cannabis in 2004, there has been a significant increase in the number of cannabis houses found in the South East region.

"During the last 12 months, Thames Valley Police has seen a marked increase in Vietnamese linked cannabis houses "In the majority of cases an ordinary terrace or semi-detached house is specifically bought or rented for the sole purpose of growing cannabis. The house is then kitted out with special hydroponic equipment which is then used to produce up to £70,000-worth of cannabis every 11 or 12 weeks.

"These factories can cause thousands of pounds worth of damage to the properties. They also pose a danger, as in many cases the electricity is by-passed which could cause electrocution or even a fire. It is also known that in some cases, booby traps have been left in the houses.

"It is in the landlords' interests to keep a close eye on their property and report anything suspicious to the police."

Over the past 12 months police found 69 factories in Berkshire and 28 in Milton Keynes and Buckinghamshire.

Anyone with information on a suspected cannabis factory should contact police on 08458 505505 or speak anonymously to Crimestoppers on 0800 555 111.

How to spot a cannabis farm: - The windows of the property are permanently covered from the inside - Visits to the premises occur at unusual times of the day or night - People often do not live in the premises and only visit to maintain them - There may be a vent through the roof or a rear window - There may be a pungent smell coming from the premises - There may be noise coming from the equipment such as cooling fans in the premises.