South Terminal is a S**hole, granted, but Flybe are aware of this, it embarasses them as much as it does everyone else, and I do believe that the Flybe top brass are trying to get the airline over to North Terminal as soon as they can. It's just not that easy. What makes South Terminal so bad is a mixture of lack of investment by BAA, the Ryanair/Easy volumes of traffic that come in waves and overpower the security area that was never designed to cope, plus the huge volumes of pax Virgin put through at certain times of day.
The Terminal was never designed to cope with this volume, and is straining badly.
Time will tell.