On a return from Berwick a few years ago, on a very hot day, I got on an old slam door train, it was bliss. The lovely guard lady said because it was hot, she was leaving the windows open, so there was a cool breeze through the train. Lots of legroom, and comfy seats.
Sadly, it broke down just outside Newcastle, so we were backed into the station, and transferred to the next (modern) train - two trainsworth of people on one train, and aircon that couldn't cope...