I can think of ABZ, BHD, NCL (may require some timing), and GLA - all of which you can freely exit from the airisde departures area to landside without any check. part of that is related to those airports not having any airside connection routes - i.e. everyone airside has originally come from landside only rather than directly from another inbound flight.

however, for all airports, if you have arrived from an international flight you will need to exit landside via immigration and then back through security to get in to the airside departures area - international arrivals are segregated and can't simply walk in to the airside departures area.

for airports which do have an airside transfer route (e.g. LHR T5) where you can do an international->international transfer without passing through immigration, there is no free flow exit.