Most cannabis used to be imported illegally from exotic places like Morocco or Nepal, but by far the majority smoked nowadays is grown in the UK.
It is not uncommon for the police to find 'grows' on an almost daily basis, often following tip-offs from disgruntled neighbours, but also by the police's own helicopter flying high overhead using its herbal imaging camera.
In this episode of Neighbourhood Blues, Humberside police trace a cannabis farm to a terraced house, and the neighbourhood police team prepares to pay a surprise visit. Despite the number of raids they carry out, what they find is still an eye-opener.
Further south a different kind of raid is underway. Neighbourhood officers have teamed up with members of the UK Border Agency to search local businesses for immigrants, who are living or working in the UK illegally.