West Yorkshire Police have uncovered more than 360 cannabis factories in 12 months, figures have revealed.
Police found 368 cannabis growing operations in the region between April 2007 and April 2008 - the highest of all forces in the UK.
The data was released by the Home Office after a parliamentary question by Liberal Democrat MP Evan Harris.
The Metropolitan Police uncovered 289 cannabis factories, and 227 were found by Greater Manchester Police.
This was followed by Avon and Somerset Police, where 207 factories were detected. A total of 203 factories were discovered over the same period by West Midlands Police.
A spokeswoman for West Yorkshire Police said they took the use of cannabis "very seriously" and had dedicated drugs teams and a force helicopter with a thermal camera which could identify the factories through heat signals.
She said: "Through this tough stance against cannabis factories, we are making West Yorkshire a hostile environment to the organised crime groups who tend to be behind these cannabis factories.
"We do not want them in West Yorkshire and if they want to cultivate cannabis here then they run the risk of being found and prosecuted."