The terminal is indeed at capacity during the summer peak where it handles between 1.25-1.50million pax per month. This is the reason for the terminal expansion which is being carried out with work starting in February. I understand that it will be a 18-24 month build process...
In addition to expansions, the airport appears to be making constant investments, having this year expanded the outbound security area to cope with demand.
The issue here, as with many other private airport its that with airlines and passenger demanding ever lower fees, the airlines themselves generate very little revenue to run the airport. I believe in an article with PK before he left, he stressed that airline fees represented only 35% of the airports income. It is now rent of retail, consumer spending, car parking and property development (hotels etc) is left to cover the remaining 65%...
obviously in countries where airports are nationalised, this isn't an issue, but as all UK airports are privates, this isn't a shock.
as has been said in other discussions, if pax were willing to pay the fare cost for flying, this wouldn't be an issue. people are happy to pay £9,99 for a ticket on Ryanair to spain, but are not willing to spend 2 hours in a tent/airport to get there.....