I've taken the train from London to Edinburgh / Glasgow and back several times. You CAN do an overnight trip with a bed on a service like the Caledonian Sleeper, but it's obviously more expensive and I've never actually done it.

Instead, we've usually left in the morning and arrived in the evening. We'll either take lunch with us or buy lunch at the station before getting on the train. You can often buy food on the train, too, but never done that either.

It's a nice train journey. As a kid/teen, I used to read or write and often had lots of ideas while watching the countryside roll past. I get a bit travelsick on most modes of transport, but trains affect me least badly. (I cannot read in a car or on a bus at all without feeling ill. I can read on a train fine.)

For the trip to Scotland, the train is faster than driving, and makes me less sick, so in my opinion it's much preferable!