The biggest problem that you'll always find with the charter airlines, is that they cannot match the frequency & flexibility that the no-frills airlines are able to provide, and which makes them much more popular for the fairly new trend of long weekends away, or to work around awkward work dates for your days off to spend at the second home on the Costas.
The charters are beginning to claw back with some better frequencies, an easier fare structure, better websites & accessibility, but they're still usually quite a bit more expensive than the low-costs if you're flying from a regional airport (BHX/EMA in my cases of looking for cheap flights, am unaware of the London situation!) and now most carriers charge for drinks & snacks just like a loco, plus charge £15 per leg for one of the infamous awful airline food.
With some tweakings I'm sure that the charters will do well again, but they have to do more to become appealing again to the many that now swear by the work done by O'Leary & Stelios.