A big increase in the number of "cannabis factories" discovered by police has been revealed.
Figures show rises since 2004 of 174 to 672 finds in the West Midlands, zero to 53 in North Wales, and zero to seven for Scotland's Northern Constabulary.
Thirty police forces in England, Scotland and Wales responded to Freedom of Information requests from BBC News.
Organised criminal gangs, many from south-east Asia, are responsible for the rise, police believe.
The Home Office said high detection rates were an "encouraging sign".
Senior officers, government officials and other law enforcement agencies gathered on Tuesday to discuss ways of implementing a new national strategy to help police close the factories down.
Forces use different definitions for what scale of production they consider to be a cannabis "factory".
But, whatever criteria they use, all but one of the 30 forces showed significant increases over the five-year period.
Gwent Police said in the past five years the number of "factories" it uncovered rose from five to 151, while Staffordshire saw a rise from 31 to 74 from 2006 to 2008, although some of those finds involved only a few plants.
The Metropolitan Police hit a peak of 648 in 2005/06, but numbers have declined since then.
During an operation in Cambridgeshire last week, police officers raided two houses and arrested three men on suspicion of cultivating cannabis.
They recovered and destroyed 800 cannabis plants with a street value of over £500,000.
Drugs intelligence officer Gavin Guy, who was in charge of the raid, said that all the plants they recovered from such factories were known as "skunk" - cannabis with high levels of tetrahydrocannabinol (THC), which makes the drug more potent.
"If we have one cannabis plant here and it's gone to fruition and it's produced two ounces of cannabis, that is supplying 16 people in this area with their £20-worth of drugs," he said.
When he began five years ago, he uncovered one cannabis factory in the first 12 months.
Last week's raid was the fourth factory discovered in his division in a week. He expects to raid about 40 every year.
Energy company EDF estimates that it is called to shut power off at more than 500 cannabis factories every year.
Many are booby-trapped to keep out the police and rival gangs.
"There are quite a few systems they use, the most common is the electrification of door handles and windows. Electrocution is a real risk," said Garry Millington, a fire investigations officer with London Fire Brigade.
Although 10 years ago the vast majority of cannabis in the UK was imported, charity Drugscope believes that today more than 90% is grown in this country.
So far there has not been a nationally co-ordinated crackdown on these illegal factories.
A Home Office spokesman said: "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 onto our streets.
"Alongside the appointment of a full-time co-ordinator, the National Policing Improvement Agency will soon be publishing guidance for enforcement agencies to help tackle the commercial cultivation of cannabis."