Any idea why a off-peak day return from London Terminals to Canterbury Stations (it will be Canterbury West) costs £19.95 with a Gold Card, yet a ticket from Hatfield to Canterbury Stations, any permitted, costs £17.55?
Because it's not uncommon for a longer distance ticket to be cheaper than a shorter distance ticket. The TOCs are sometimes so obsessed with ripping us off for a certain route that they perhaps forget to increase the price of the further tickets!
The latter includes another 25-30 mile journey on top, but is cheaper.
HS1 is a total rip-off to/from London but beyond London it usually makes sense to use it, both time-wise and price-wise.
I live on the route of the High Speed line in Kent and make regular cross London journeys. I have noticed that for some destinations there are two fares with a supplement for HS1 but for others one fare is quoted and includes HS1.
In general:
For tickets to London (or short of London) the fares that should be called Any Permitted fares are, confusingly, called "Plus High Speed". There is no need for that at all (I don't buy a York to Middlesbrough "Plus High Speed" ticket to use a HST via Darlington!) everywhere else uses "Any Permitted". If "Any Permitted" is good enough for everyone else then it's good enough for SET.
Once you go
beyond London, you then have the normal +Any Permitted fares, but also have +Not valid on HS1 fares that are a little cheaper (and
generally not worth bothering with, depending on the final destination and the saving), but once you go beyond the 'Network Area' (former NSE area) ie. as far as Peterborough, Rugby, Swindon etc, the only routes available are +Any Permitted (plus any other routeings historically available) and there is no cheaper option to avoid HS1.
As for supplements, to clarify what normally happens for a change of route is an excess fare is charged. For some bizarre reason (I suspect it is a time-saving measure for guards, as excesses are a faff) the excess is not calculated and charged according to the usual formula (ie, half the difference in fares) but instead a standard supplement is charged, this means some people pay more than they should pay under the excess system while some people pay less.
Of course this talk of "supplements" and "Plus High Speed" routeings causes confusion as it means for local journeys on SET use terminology that is out of synch with the rest of the UK rail network, every so often someone gets confused when they are used to these fares and wants to go further.
As usual the TOCs (whether this is down to ATOC or SET I do not know) make ticketing as complicated (don't believe their lies over fares being "simple") as possible and confusing people.
I do wonder if the pricing manager at SET had something to do with this. I don't get the impression that he is pro-customer at all.