On the WCML, you have to pay ££ for WIFI unless you're in first class and even then it's patchy because the train doesn't always have a clear view for the satellite data.
> or you can just use 4G.
Down the WCML, you're lucky to get even 3G thanks to the combination of poor coverage from cell towers (not much call for them in rural landscapes, really) and the metallised glass they use on the trains.
(They did try per-carriage femtocells but they didn't help.)