For those wondering about the 5th paragraph, the direct trains between Milton Keynes and Clapham Junction (and thence to East Croydon) are part of the Southern Railway franchise.

@HenningMakholm thanks for pointing that out. I added it to the question.

How far in advance did you book? There's been some noise over the summer about GTR (the holder of the Southern franchise) pseudo-canceling trains by removing them from the electronic timetables a few days before they were supposed to run -- that way they won't show up as cancellations in the official statistics.

Could you also confirm that these were Advance tickets (ie, tickets bought in advance for a specified train or combination of trains), and not merely open tickets bought well before the date of travel?

@MadHatter yes, it's an Advance Single. I added a photo of the ticket.

I am now chatting to trainline's support. They don't understand the problem and say I should use a form on their website that doesn't exist, and claim because I used the ticket they can't refund it. Which is probably correct, but I want compensation.

@simbabque: It probably doesn't help the support person understanding you if you keep insisting the train "was not canceled". On the contrary, it sounds like it was very canceled, to the point of not even appearing on the departure screens.

@Henning My understanding is that a cancelled train shows as cancelled. But when I was at the platform there was no evidence of there having been a train scheduled, hence it couldn't have been cancelled.

@simbabque: Well, if you would rather insist on that narrow meaning of "cancelled" than actually convince someone that you're owed compensation, that's entirely your decision ...

And since your insistence that Southern did nothing wrong comes in face of mountains of evidence (in your own question) that Southern did actually cancel the train you were hoping to travel on, the only one who is to blame for your failure to claim compensation from the TOC that cancelled your train is yourself.

@simbabque The train must have been scheduled at some point or it wouldn’t have shown up in Trainline’s system (their T&C explains that they take a feed from the operator). Henning Makholm is right - Southern must have withdrawn the train from service after you bought your ticket; it’s semantics but I imagine somewhere buried in their T&C there’s a technical difference between ‘withdrawn’ and ‘cancelled’ depending eg on how soon in advance it’s done - using the latter definition probably helps massage their performance figures

It does look fairly likely that you have been royally screwed over by Govia Thameslink Rail, wearing their Southern Railways hat. Their recent performance has been so dire that heads have rolled, so you're not the only person in that position. Claim from Southern.

@HenningMakholm I insist on that difference because I want to avoid being brushed off by them later because of their own definition of canceled. Maybe I need to be the naive customer.

For what it's worth, that train is listed as normally existing in their paper timetable southernrailway.com/travel-information/plan-your-journey/-/…

@simbabque all the evidence suggests that the train was scheduled when you bought your ticket, but cancelled at some point before it was supposed to run. Treating it as a cancelled train is not being "the naive customer", it's being a rational person. If Southern try to hide behind some esoteric definition of cancellation, let them tell you so and then base your subsequent response on that information. Redefining cancellation to exclude what happened to you and then using your invented definition to demand compensation from the wrong company is not an effective way to avoid being brushed off.

I have claimed with Southern, but I believe all I will get is a part refund because I was pretty much a little under two hours later, disregarding the unpleasentness of having to take a replacement bus and the tube. I will keep this updated with the response and not accept an answer yet until there's an outcome.

Which part of "not refundable" (printed on the ticket) don't you understand? If there were engineering works on a main line route in the UK, there would almost certainly have been some "required connecting services" to cover the gap in t he rail network (for example a road coach service to an alternative station). It's the traveller's responsibility to find out about such things before starting a journey, IMO - it's not as if somebody suddenly decides to do major engineering work without any warning of the disruption.

@alephzero this is not about refunding, but about claiming compensation for being delayed. There were alternate routes available via Edinburgh from Glasgow to get to where I needed to go, but I didn't know about them because the re-seller I bought my ticket from did not show information about the delays. Not even on the day I travelled. My ticket was for this connection, so I couldn't go via Edinburgh to King's Cross. The problem is that Southern suddenly decided to not run trains. See what the various answers have discovered.

@Flexo what does the credit card have to do with it? I could request to undo the transaction, regardless of the amount. But I don't see the legal grounds to do that in this case. I don't want to get my money back. I want the money I'm entitled for not receiving the promised service.

@simbabque which.co.uk/consumer-rights/regulation/…

your credit card company would be jointly liable with whoever your contract was with, if the ticket was > £100