Hello. I'm trying to book a return journey from the above stations leaving on 7/05 returning on 20/05. leaving both days after 11:00. I would prefer to avoid the obvious route via London and the underground. National rail timetables offer an alternative route via Redhill - not a great deal of difference in journey time or price and my preferred choice. When I go on through to the GWR site to make the booking I get a notice saying "We're sorry but this ticket is no longer available".
The links between the National Rail site and the various retailers aren't that reliable. I would have suggested using a different retailer with it, but I've no idea how you would do that with their new user interface.
Most retailer let you request journeys via Redhill directly, but I did have trouble with gwr.com when I tried there. Its main booking thing ignored a "via Redhill" option but not an "avoid London" one. Its "accessible booking tool" was better, and respected "via Redhill".
The through fare is equally valid via London (including Waterloo-Reading) and for your dates there seems to be little advantage in splitting or in using Advances
I don't know if Proc.amp wishes to reduce the cost, but the options there would depend on the situation. For instance, someone with a Network Railcard or Annual Gold Card could save money by buying a "via Gomshall" Tonbridge-Blackwater and a "not via London" Blackwater-Taunton ticket (as the first ticket could be discounted using the railcard). It wouldn't help much for someone who didn't wish to use either.