If you want absolute cover for every possible transport eventuality outside the control of National Rail, before you even get to a station, then buy the appropriate walk-up fare when you get to the station.
Otherwise there's Advance Purchase. A cheaper, more restrictive product.
Otherwise there's Advance Purchase. A cheaper, more restrictive product.
The problem is that it's not an either/or. GWR▸ (Great Western Railway) have deliberately chosen to replace affordable, flexible, walk-up tickets with restrictive Advance tickets. That's what happened here on the Cotswold Line: new, draconian peak restrictions were introduced for flexible tickets, and Advances introduced as a sweetener.
Advances don't generally suit my circumstances, so since these fare changes, I simply travel less frequently to Paddington using GWR. On the occasions that I do, I either split my ticket to get round the off-peak restrictions, or go to Marylebone instead (thank you, Chiltern, for retaining sane fares). Oxford Parkway is becoming surprisingly popular for passengers from the Charlbury area, more than I originally expected, and GWR have only themselves to blame.