I worked out that the particular round trip, for myself and my wife, would cost near as dammit the same whether I flew (2POB, aircraft + fuel costs + airport charges) or took the train (2 return off-peak tickets); specifically about £320.
I suspect that the flying would as well as being quicker and more fun, attracted less subsidy from other taxation than taking the train, even with a share of anotherthing's pension fund!
G