You are absolutely correct and I know that Dorset, Essex and Somerset & Avon Police also do not actively seek it.
I have been told by the Police & Crime Commissioner of Essex himself "We have absolutely no interest in that. We expect 3 seperate complaints about smell before we'll even send an officer round to knock on the door to have a friendly word, but no warrant and no power to caution at that point"
It may also interest you to know if you don't already that UK police forces have actually lost their powers to stop and search somebody on the smell of cannabis alone as probable cause (established by collapsed case law). Too many cases of people being ejected from festivals and subjected to search and detainment for the smell of weed where they genuinely haven't got any on them, it was somebody else walking past etc.
A smell alone is not probable cause. The officer who told me that said it is a problem for them as it was their chief way of getting knives off the street - the chances are some stinky weedy person in the street also has other drugs and weapons on them is quite high. Good news for recreational growers and smokers, but a double edged sword for the forces.
How sweet it is to be so far on the inside you're above suspicion. That's what it is to be Silvio Dante
*I should also say that the legalisation of cannabis is quietly making its way through Parliament:
https://services.parliament.uk/bills/2017-19/legalisationofcannabismedicinalpurposes.html