It used to be the case that CRAs only supplied information to organisations that provided it to them. For example, banks furnish the CRAs with monthly updates on all customer accounts, and in return get to access all your most private finanical information from all other contributing organisations. So how do councils fit in to this, I wonder? They don't supply anything - not even the electoral role. That is TAKEN by the CRAs. Maybe the rules have changed and anyone can now buy information from these parasites - anyone know?
Look at their websites, or marketing materials.