If you don't feel like spending many hours in a train, you can consider travelling by plane. Especially if you have the possibility to book in advance, flying to London can be definitely cheap.
What are the departure and arrival stations in Glasgow and London?
The trains to London can leave from Glasgow Central or Exhibition Centre (Glasgow) and arrive at London Euston or London Kings Cross.
How long does it take from Glasgow to London and when do the trains leave?
On average, it takes 5 hours and 34 minutes to get to London by train, but you will need 4 hours and 57 minutes with the fastest trains. The first one is available at 06:10, whereas the last one leaves Glasgow at 08:10.