Giles,
The published figures are available on the Airport website under publications/ operations.The figure there shows an increase from 2012/2013 of £6.90(domestic) £10.56 (Int) to £7.09 and £10.84 respectively for 2013/2014.
As you say the airlines have confidential agreements with the Airport and are obviously not paying these figures.Interesting that the yearly increase does seem minuscule though.
By the way Norwegian moved to LGW a while back now from STN.
Agree that Ryanair haven't really shown any desire to expand from LTN in a while.They could do more with a/c from overseas bases if they wanted but I guess they will only put the pax numbers through LTN that have been agreed.
As I have said before on the threads they showed no desire to base a/c at other London airports when Easy was expanding deciding all eggs in one basket at STN was ok.Now all they have to do is agree with MAG at STN - toys out of pram comes to mind again.