POLICE are investigating links between a series of drug finds in the North-East and an international crime ring led by a Vietnamese gangster.

More than 1,500 cannabis plants were seized from a number of homes in County Durham and detectives last night admitted their investigation was continuing "further afield".

The development came after it was discovered that criminal gangs were renting or buying properties elsewhere in the country for the sole purpose of growing drugs.

Detective Inspector Billy Hugill, of Durham Police, said he was aware of newspaper reports of criminals in London growing cannabis in empty homes, but did not want to draw any conclusions about the raids in County Durham.

He said: "I am aware of the stories but, at the moment, there is nothing to say they are connected.

"I can say that our investigations are taking us further afield.''

Three of the men being held in connection with cannabis factories found in County Durham are Vietnamese, and two of them gave London addresses.

Durham Police's Operation Applejack started only days after Assistant Commissioner Tarique Ghaffur, the head of the Metropolitan Police Specialist Crime Directorate, admitted police had a problem with Vietnamese gangs flooding the streets of London with high strength home-grown cannabis, known as skunk.

The gangs are reportedly making millions of pounds by renting houses from unsuspecting landlords and converting them into sophisticated cannabis farms - similar to those that were discovered last week in Bishop Auckland, Coundon, Ferryhill and West Cornforth.

Last week, five separate cases involving Vietnamese drugs gangs were being heard in a London court in one day.

A 17-year-old, who was convicted of running two cannabis factories, told a London court that he had been paid £200 a week to look after 270 plants in two houses.

Assistant Commissioner Ghaffur said: "We have seen a growth in cannabis cultivation in recent times in London and we have experienced a tendency for this sort of crime to be committed by a number of communities, including small elements within the Vietnamese communities.''

Other reports describe a Vietnamese farming operation uncovered in South London in which four houses yielded harvests of 40kg of cannabis, worth £120,000, every six weeks.

It is thought that similar operations have been discovered in Liverpool, Manchester and Birmingham.

Drug information charity Drugscope said that it was aware of the apparent increase in the growing of cannabis, but was not sure about the Vietnamese connection.

A spokesperson for the charity said: "Police from various forces have recorded an increase in raids and seizures, but there is no proof that the use of cannabis is on the increase.

"Although cannabis has been downgraded to a class B drug, the penalty for supplying and trafficking has been increased. Cultivating it is still illegal.''

It is believed one of the reasons for the setting up of more sophisticated factories in this country could be because it is no longer illegal to buy cannabis seeds or growing equipment, despite it remaining illegal to grow the plant.

The spokesperson for Drugscope said: "Evidence suggests that the number of young people using cannabis has levelled out and is possibly falling. But it is appearing easier to grow it rather than import it and we fully support the police in closing these cannabis farms down.''