I’ve been frustrated by this for years, you just know that if there was a mobile data deadzone on a motorway they’d fix it immediately.
replyMeanwhile on the train 30 miles from London, nothing.
Here’s a hack, get yourself a cheap eSIM data only plan from an alternative UK network (VOXI, Talkmobile etc) if you main network doesn’t have connectivity; they will!
replyThere's even eSIMs specifically marketed as being a "backup" esim, with coverage on _all_ UK networks.
replyAt least on my android, you could set the second esim as a "backup" that it would switch to for data if the main one lost connection (it took a few seconds, so it wasn't an "always connected" experience, probably because the phone wants to save power)
Lots of options if you search for "esim UK all networks".