No, GTR treats these brand restrictions as if they were TOC restrictions, and TOC restrictions can't be excessed away.
As anti-passenger as that is, there is a certain logic to it if you travel on the wrong TOC, since if you travel from London to Doncaster on Hull Trains with a Grand Central only ticket, then Hull Trains won't have received any of the revenue from the ticket you bought, so you can see why they would want to sell you a brand new ticket and not take account of the fare you've already paid. No such logic applies in this case, however, because GTR absolutely has received the revenue from the ticket you bought in the first instance, so even if you accept (which I don't) that it is legitimate for them to charge a premium for GX, there's no obvious reason why excessing people from Thameslink Only or Southern Only tickets to Any Permitted wouldn't achieve that objective. Nor is there any reason why the premium tickets shouldn't be valid on Southern and Thameslink branded trains.
The only reason to double-charge anyone would be if the objective wasn't to charge a premium for the non-stop express trains, but to confuse passengers, many of whom are unfamiliar with British railway ticketing, hope they make a mistake and fleece them as much as possible when they do.
It could be the GX revenue is falling off a cliff and the DfT are putting pressure on GTR to improve the numbers.
I do a fair amount of off-peak travel between Brighton and London:
- GX patronage is best described as 'quiet' which is nice, but doesn't justify the additional fare if you don't need to go to Victoria as your final destination because Thameslink offers better connections to other parts of central London: even going to Paddington is usually easier and faster via Farringdon than taking the Underground from Victoria.
- For most practical purposes GX isn't any faster (but see my question below). Pre-COVID the GX trains overtook slower services at Haywards Heath.
Here is a related query for the fares experts on the group:
From Brighton to London Thameslink (a journey I make quite frequently) there are three ticket options:
- Any Permitted
- Thameslink Only
- Not London Underground
Questions:
1. The last two cost the same and, after railcard discounts, are a bit cheaper than
Any Permitted so what is the point?
2. For a journey back to Brighton it is sometimes quickest to use Thameslink to East Croydon, then Southern to Gatwick or Haywards Heath and GX for the rest of the journey to Brighton. This can save around 15 minutes on arrival at Brighton. Is there any reason why I would be challenged for using the cheaper
Not London Underground ticket on the GX or Southern leg of such a journey?
Maybe worth adding here that there are usually announcements on GX services leaving Brighton about ticket validity and I'm pretty certain I've heard them say that London Thameslink tickets are not valid. This is obviously true north of Gatwick but it's unclear what the rules are between Brighton and Gatwick.