@bestdeadends I've not tested it, but in exchange I'll share this tip from railsmartr.co.uk london-to-cardiff/
The best advice that we have for finding a cheap London to Cardiff train is to aim for the trains that terminate at Cardiff Central. These trains usually leave London Paddington at 18 minutes past the hour. The trains at 48 minutes past tend to be busier, as they continue to Swansea or Carmarthen.
@rhysw @bestdeadends I was just to thank Rhys for this excellent advice, then I remembered that we catch the London train *in* Carmarthen. At least it’s quiet at our end!