The building, on an industrial estate in Kirkintilloch, was used as a front by a suspected drugs gang.

Officers raided the property in Woodilee Road, in Woodilee Trading Estate, and discovered about 2500 cannabis crops in dozens of industrial containers.

Four men have been detained.

The factory is next to a car washing business.

One witness, who saw police carry out the raid yesterday, said: "It is just an old building, you wouldn't look at it twice.

"And you definitely wouldn't think it was being used as a drugs factory.

"I heard the police helicopter out earlier about 10am."

Chief Inspector Roddy Irvine said: "An extremely vigilant member of the public alerted us to this property, which has led to this operation.

"We have recovered about 2500 plants, which are estimated to be worth £750,000.

"Officers also detained four men at the scene.

"This operation has caused significant disruption to the criminal cycle, and it is reasonable to assume these drugs would have made their way into our communities and caused harm.

"It is not possible to say what the long-term effects of our operation will have on the street value of drugs, but this is a very significant find, by anyone's standards.

"I would ask anyone to report any inci- dents of suspicious behaviour."

A police spokeswoman said the force had uncovered a "significant cannabis cultivation".

The find came just 24 hours after police found £55,000 of drugs – believed to be cocaine – in a property in John Street, Kirkintilloch.

A 25-year-old man was arrested in connection with alleged drugs offences.

Police are not linking the two incidents.

rebecca.gray@ heraldandtimes.co.uk