Is surbiton in south west london or surrey?

Administratively, Surbiton is part of the London Borough of Kingston-Upon-Thames. It is a part of Greater London. However, historically, it was a part of Surrey. The ancient counties still exist but not as administrative units. The same applies to other parts of London. Even Rotherhithe was in Surrey once.

Just because there are artificial lines to mark the Met Police force area and the Mayor of the GLA jurisdiction, doesn't change the fact that Surbiton is positioned on physically Surrey county territory, which does extend as far northeast as Lambeth, Rotherhithe, Peckham and Norwood if you consider sufficiently far back: before the most recent 1965 boundary change back to the designation of the County of London in 1889. However an argument does exist for BOTH geographical designations, the "southwest side of London" and the "original territory of Surrey". But think about it this way..if the occasional mooted proposal to simplify the GLA administrative boundary to correspond with the M25 route were at some point brought into effect, would that mean that currently non-Greater London locations such as Cobham and Walton-on-Thames are to be regarded as essentially "London" and not as Surrey at all? Such a proposal would be no different from the designation of the Greater London which exists now.

It's difficult to give a definitive answer. I come from Carshalton and identify about 70% with Surrey and about 30% with south London. I stress south London specifically, not proper actual bona fide London-London. If you talk in terms of southwest London specifically, that creates further ambiguity over what can count as being SW. The limit could extend as variously far eastward as New Malden, Worcester Park, Mitcham or even Norbury. Can I also add that Surbiton clings to the edge of the Greater London area. Quite a large part of Surbiton (around Long Ditton) is not in Greater London at all but undeniably in the Surrey County Council area.

It all depends of what you define as "London" or "Greater London". Technically speaking Surbiton is in Surrey along with other places such as Croydon, Kingston, Richmond, Sutton, etc as it doesn't have a London Post code, unlike Wimbledon which does have a London post code (SW19). However many people including those in power, use the M25 motorway which orbitnates London, as the boundary and that any town that falls within it is in London, regardless of it's postcode. Furthermore the media uses it to sensationalise stories, for example is I said there was an armed robbery in Woodford Green, Essex, it would not grab half as much attention if I said there was an arm robbery in Woodford Green, East London

Same with lots of places...Is in GREATER LONDON and has a SURREY address....They tend to mix and match..........NOT only LONDON. Live now in Greater Manchester....Places in the north of the conurbation have Lancashire addresses, and in the south Cheshire ones, BUT are NOT in those counties, despite the postal addresses. Here too, one minute someone will say Bolton in Greater Manchester and the next....... in Lancashire......