Am I remembering correctly that there's nothing in the Fire Services Act to specifically say we are obliged to inspect premises?
the FSO states
Enforcement of Order
26. —(1) Every enforcing authority must enforce the provisions of this Order and any regulations made under it in relation to premises for which it is the enforcing authority and for that purpose, except where a fire inspector or other person authorised by the Secretary of State is the enforcing authority, may appoint inspectors.
this is probably the closest you'll get, it mentions we must enforce the order but not how.
some may argue that to enforce you need to periodically inspect, others may say we'll deal with each premises as and when they appear on our radar (i.e. AFR or after fire inspection).
this is probably why different brigades are enforcing the order to different standards.
personnally i think there should be a national standard, to have an act enforced differently just because of your geographical location to me seems ludicrous.