First, what are counties? -- This word refers to an administrative area comparable with the French département. And the group of counties that surround London are called " the Home Counties", possibly because of the Home circuit of the itinerant Assize Court (= in the XIXth. century, the places that London Assize judges could visit in the daytime and still be able to come back home at night !).
The list includes: Buckinghamshire (Bucks), Hertfordshire (Herts), Berkshire (Berks), Kent, Surrey, Essex, Middlesex, and Sussex.
They are also called "London and the South-East", the "London commuter belt", or the"London metropolitan area".
They are described as conservative (culturally, and politically: it is a tory stronghold [Fr.: un bastion conservateur]). The "home counties accent" is easily recognizable (and often heard on the BBC !).