A heat-seeking helicopter - using technology often associated with military operations - is being deployed across Norfolk in a bid to clampdown on illegal drug factories.

A heat-seeking helicopter - using technology often associated with military operations - is being deployed across Norfolk in a bid to clamp down on illegal drug factories.

Police revealed the tactic as they spoke of raids which have seen five cannabis-growing operations closed down in Norwich, Yarmouth and King's Lynn over the past three months.

The equipment installed in the force helicopter detects excessive heat coming from properties which can indicate the use of sophisticated lighting systems used to cultivate the plants.

Det Chief Insp Colin Pearce said: "It is one technique which we can use to gather intelligence when we suspect a property may be involved in drugs production.

"It is common for properties where drugs are being produced to be fitted with quadraphonic lighting which accelerates growth.

"It uses large amounts of electricity and can present a rise risk.

"Using heat-seeking technology from the air, it is possible to detect such properties as part of our intelligence-building."

Mr Pearce refused to comment on whether this technique had been used in the recent raids as all five are yet to be taken to court where such information could be used as evidence.

He said operations to close down such factories were continuing.

In recent years drug producers are believed to have relocated to areas like Norfolk following the Metropolitan police's success in clamping down on such activities.

"Often criminals will rent a house above the going rate so that landlords do not ask questions about their activities," said Mr Pearce.

"After about a year they will suddenly move elsewhere, sometimes leaving the property unsafe."

Last month 400 cannabis plants with a street value of tens of thousands of pounds were seized from a house in St Martins Road, Norwich.

Earlier this month 600 plants worth about £60,000 were seized from two premises in Southtown Road, Yarmouth.

These followed earlier raids in Norwich and King's Lynn.

Three of the raids were based on information from suspicious members of the public.

Signs to look out for include curtains constantly being closed; lots of noise when people move into the property but afterwards nobody seems to live there; strange smells; paper put up inside windows; excess heat; and condensation on the window or the brickwork of the house.

Mr Pearce said: "We are extremely pleased with the results that have come in over the past few weeks and our work so far will send out a clear message that cannabis production is a serious offence and that offenders will be brought to justice."

Anyone who suspects such activity should contact Norfolk police on 0845 4564567 or Crimestoppers anonymously on 0800 555111.