And if you take the train from London to Glasgow, it is currently £120 for a single ticket, whereas I can book on British Airways for a flight tomorrow for £74.
Should probably be a bit fairer to the train as you can get better deals than that and pay a lot more on BA. I've paid £80 for a first class return and I've paid more than £250 return on BA (both London - Glasgow).
But yes, the train can be terrifyingly expensive if you can't pick and choose your time (though I also find it more productive - no putting away your laptop for take off, no security, just sit down and do stuff).