I stand corrected about Croydon! I'm surprised, though, because many of the towns on the outskirts of London still have their counties in their postal addresses - Morden (Surrey), Harrow (Middlesex), Bromley (Kent). If you look up Beckenham online, it's always listed as being in Kent, and that's only a few miles south of here. I wonder if there is a difference between the formal county boundaries and what the post office recognises for addresses.