FGW seems to have a special timetable evry Sunday. Currently (until 22 July)
Sunday long distance departures from Paddington a
xx07 Bristol TM
xx12 Cheltenham (even hours 1212 - 1812)
xx27 Swansea

Interesting. My train, the xx27 was the Temple Meads service (the 1727
which actually left was supposed to be for Weston-super-Mare, but was
terminated at Temple Meads with a transfer to local services.

We stopped at Slough, Twyford, Reading, Didcot P/way, Swindon,
Chippenham, Bath Spa & Bristol Temple Meads. It was announced as
"possibly" stopping Nailsea/Backwell & Yatton, but didn't get past Temple M.