None of whom are "the police".
The NPCC are a company limited by guarantee, and about a half of them aren't even police officers. Lord knows who the others think they are.
I've served in two different forces and worked for extended periods with two others, and none of them use this tome. Get over it.
Being a limited company is immaterial. There are around 100 limited companies directly relating to various police forces/associations in the UK, including the Police Federation of England & Wales which, I believe, is the staff association for "police constables, sergeants, inspectors, chief inspectors and special constables in the 43 territorial police forces in England and Wales". Maybe they're not policemen and women?
According to the NPCC web site their membership consists of the Chief Constables of (as far as I can tell) every police force in England, Wales and Northern Ireland plus some non-civil police forces and the National Crime Agency and the College of Policing. Maybe they're not policemen and women?
I have contacts in the roads policing teams of eleven English police forces and they all use Roadcraft for training and as a reference book for driving standards. I'm over it.