A (very) quick look at fares ... Singles from Craven Arms to Worcester Foregate Street and back, period (not day) return from there to Oxford and single Oxford to Paddington (peak) and back (off peak) add up - but subject to checking - at £153.50, valid for your trains. Still more than the £103.00, but far less than the £237.60.
Thank you for that help with split ticketing - will play with that more at the weekend. That's a big improvement and £20 better than I was getting with Avanti. Realistically I would like to keep my return as PAD» (Paddington (London) - next trains)-NWP-CRV so I get home for dinner on a Friday.I also noticed a very interesting anytime period return £111.40 fare Craven Arms to London via Warminster and Salisbury!
It's indeed an attractive fare, but at 5hr 25m for a journey that can be done in 3hr 15m it means it is only for the time-rich (which sadly I am not, yet)!