Class "F" ADR's are now defunk....Class "F" now been replaced by Class "E+" As for the Stobart mentioned earlier if the company choose to operate in class "G" airspace and there is not a radar unit willing or able to provide some form of radar service, "Traffic service" or "Deconfliction service" then it will be down to the appropriatte FIR sector to provide them with a "Basic Service"
Slightly differant in Scotland as the FIR sector 119.875 only operates at FL055 and below, is manned by FISO's so only a Basic service will be given. Above FL055 then the Scottish control radar sectors can subject to traffic density provide off route traffic with a radar service.