The Post Office still recognises Middlesex, which disappeared in 1963, despite Ernie Marples' postcodes, and which at that time included Staines before it was Staines-on-Thames. Is Kingston upon Thames in Surrey or (Greater) London.
Middlesex as a county sadly expired in 1965 with the implementation of the 1963 Local Government Act, with most of it going into Greater London, and the remaining bits parcelled out to Surrey, Berkshire and Hertfordshire. However, it lives on in popular lore, and even today many inhabitants can't take seriously the idea of Staines, Ashford, Sunbury, etc, being in Surrey -- they're on the wrong side of the river. I was at Waterloo the other day and the tannoy announcement for 'Ashford, Surrey' seemed so
wrong. Middlesex continued as a postal county until 1996, although considerable chunks had already been subsumed into the London postal area, set up in 1889. 'Staines-on-Thames' is a council publicity stunt that many inhabitants find risible. However, because of the frequency of flooding, 'Staines-in-Thames' is jokingly seen as a suitable name.
Kingston was the county town of Surrey until 1965, when it became part of Greater London, then Guildford became the county town. Oddly, much of the Surrey administration remained in Kingston until fairly recently. Kingston and neighbouring Richmond, also in Greater London from 1965, are still seen by older residents as being in Surrey.