Nyaarrrghhhhh!!!
Don't worry, this isn't a "can we change the date?" Nyaarrrghhhhh, but bloody hell thetrainline.com's getting on my tits today. First time in, it told me there were no trains between Glasgow and York. Then I went in again, and it found some, and let me chose my train, and showed me the ticket prices, and then I decided to see if I could work out how the shopping basket worked, and somehow ended up losing the booking (for future reference, if you get to stage 6 of the booking process, the ticket is added to your basket. That's the ONLY WAY). THEN I went back in, and the ticket I'd booked wasn't available on the train I'd booked it for, but I managed to book another ticket at the same price at something approximating the same train*, tried to pay, and it didn't get to the confirmation screen. Phoned support, they confirmed that payment hadn't gone through, and I should try again. Tried again, got a message saying that payment hadn't been authorised. Tried another card. Same thing. Tried another card. Same thing. Gave up, and I'm going to go and speak to a human being at a train station to see if I can get the tickets I'm after. Useless bastards.
*Original was 9:30 Glasgow -> Edinburgh, 10:30 Edinburgh -> York.
Second attempt was 9:20 Glasgow -> York, which is the same train as gets to Edinburgh at 10:30. Madness.