Booking a month in advance, with one check in bag, and checking in at airport.
Glasgow to London 20th March 2008 (chosen at random):
Ryanair:
£43.23 STD 1015z (Fare £9.99 Tax £18.33 Baggage £9.00 Ins £5.91)
Easyjet:
£33. 98 STD 0915z (Fare £9.00 Tax 15.00 Baggage £3.99 Ins £5.00)
BA:
£41.60 STD 1030z (Fare £11.00 Tax £30.60 Ins inc)
The prices are all getting rather close....I know who I'd rather fly with.
