Spud, you are quite right they are not all low cost seats!. All of the LCA's that I am aware of make it quite clear that the earlier you book, the cheaper the seat, a very simple formulae, and very well publicised.
for example
easy today LTN-ABZ return tomorrow 01 Aug 143 up 144 down total price 166.30 gbp (cant book 141 its already gone)
same trip tue 27th Aug up on 141 down wed 28th on 144 total price 37.30 gbp
no offence spud, but see how it works?
By the way GNER rail return up today back on the first KX - ABZ £196.00 standard fare, you can get it much lower if you book early though
