After moaning about on-train Wi-Fi three years ago, sad to report that it is still the same hit and miss affair.
One trip on the east coast mainline (a standard bearer for long-distance travel in the UK because it runs for 520 miles) can be fine, another trip back the way you've come can be near awful. Let's define 'near awful' more specifically. Not downloading Torrents or watching video after video on YouTube, we are talking about very slow access to almost any website you care to mention.
Perhaps that's not awful, but it's not the experience that Wi-Fi was invented to provide. The question that hangs over this is what are the variables that make the difference between one good, well-connected journey, and another, somewhat disconnected one?
If it's the Wi-Fi access point on the train then I'd suggest they fit standard Ethernet ports beside seats. If (as I suspect) it's some kind of contention between the train and the line uplinks, then something else is at the root of it.
One rail franchise change from GNER to National Express later and travellers are still not much further on than they were in 2006. Is that why they stopped charging for it?
Arguably, the one advantage of charging was that they could have, if they had chosen to, used the more involved sign-up process to distribute a proper encryption key. That's a totally separate ‘lack' - there is no security for anything you do on a train Wi-Fi unless you slow your link down even more with a VPN.