London Terminals - Ashford International has a mapped Permitted Route between London St Pancras and Ashford International by map
HS.
This route may be used without additional payment by valid tickets routed "via Any Permitted" (e.g.
Edinburgh - Ashford International route + Any Permitted) or "Plus High Speed" (e.g.
London Terminals - Ashford International route Plus High Speed).
Other tickets valid between London Terminals and Ashford International (e.g.
London Terminals - Ashford International route Not Valid on HS1 or
London Terminals - Ashford International route via Haywards Heath) may be used on the Permitted Route shown on map
HS upon payment of an excess fare in accordance with
NRCoC Condition 13(e).
I can therefore see no way that a Penalty Fare could be sustained if issued to someone travelling by HS1 with a ticket valid in all respects except the route, and I'm inclined to think that the assertion by
LM__ in
this post that Penalty Fares issued to passengers who are off-route are "
one of [SouthEastern's] biggest earners" is wide of the mark. No such cases have been reported on this forum.