Dave Arquati wrote:

In this manner, introducing PAYG on, for example, Crystal Palace to
Victoria would mean that passengers simply travelling to the vicinity of
Victoria could buy the cheaper CDR, whilst those travelling on via Tube to
somewhere like Oxford Circus could use PAYG and avoid using two tickets.

At the "State of London" debate today I went to the session on transport
with Peter Hendy (TfL Commissioner). One of the audience raised the example
of travelling from Clapham to Waterloo - from Clapham Junction a CDR with a
Young Person's Railcard is about £1.60 wheras on Oyster PAYG Clapham Common
to Waterloo and back is £4.00.

Hendy said he was surprised that there are any places where National Rail
fares are cheaper but declined to give explicit assurances that fares will
not be pushed up if/when PAYG is rolled out on National Rail.