20 cannabis farms and factories were discovered by police every day last year as the downturn saw more drug users switch to growing their own products. Senior police chiefs revealed that last year they seized drugs which could sell for £100 million on the streets. Officials said the size and scale of the farms were reducing as criminals producing cannabis were spreading the risk and minimising losses by employing a large number of so-called 'gardeners' to manage small sites across multiple residential areas.