When I was living near Clapham Junction I often travelled to
Sittingbourne in Kent. Sometimes they would (try!) to sell me a 'Not
via London' ticket which is rejected by the barriers at Victoria (in
that case I would just buy a single to Battersea Park...). IIRC the
price is the exactly the same for a via London ticket but I never could
work out how to get from CJ to Sittingbourne without going through
Victoria (prehaps it's possible by some obscure route to get to
Bromley?).