Search: Cannabis factories
The number of cannabis factories raided by police has risen sharply in the past five years.
Twenty-nine forces told the BBC they had uncovered more of the drug being grown, including Gwent which detected no factories in 2004 but 151 last year.
The largest force in the UK, London's Metropolitan Police, reported an increase from 206 to 654, while West Midlands saw a rise from 174 to 672.
New guidance has been drawn up by the National Policing Improvement Agency to tackle the burgeoning problem of cannabis cultivation.
A national cannabis co-ordinator has also been appointed to share information and best practice between forces, a Home Office spokesman said.
He added: "We are determined to make this country a hostile place for criminals involved in cannabis cultivation. The high levels of detection of cannabis farms, as revealed in these figures, are an encouraging sign and demonstrate our commitment to catching those who bring cannabis on to our streets.
"Upgrading cannabis to Class B enables police to focus more on tackling supply of this illegal and harmful drug. We are working hard with the Association of Chief Police Officers to build a better national picture to deal with this problem more effectively."
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Thirty forces answered a Freedom of Information request from the BBC about the number of cannabis factories raided.
Three forces found no factories in 2004 but by last year North Wales had 53, Scotland's Northern Constabulary seven and Staffordshire 59.
Cannabis is the most commonly used illegal drug in the UK, although, according to the British Crime Survey for 2007/08, the number of people who have ever taken it has stayed roughly the same in recent years. The number of people who said they used it in the past year has decreased steadily since 2003/04.
