For example, Enfield council ( enfield.gov.uk ) is using Google's ad server (DFP) set to show only internal ads. All their advertising is for cross-promoting projects and sites that Enfield council is involved with, including pest control, social lettings, a publicly-funded golf course, school meals...
It's not showing ads from GDN (Google Display Network) or elsewhere, it seems to only show these internal promotions.