TheOneKEA ) gurgled happily, sounding much like they
were saying :

Simple: Oyster validators at every single National Rail station inside
the Zones.

Oh, if only.

I needed to go from Vauxhall to Waterloo recently.

Easiest way? Mainline, right? One stop. Takes longer to type this than the
flamin' journey.

No. The Oyster validator told me to seek assistance. I did. Nope, I've only
got (more than sufficient) PAYG on there, and need at least a weekly
Travelcard.

The bus took ages to arrive, then far longer to actually complete the
journey, plus the walk from where it terminated to Waterloo station itself.