Changes to air fares on Belfast London naturally will increase quite naturally. Supply and demand and the airlines approach to yield management (I.e. First batch of seats at low prices hence if the plane is heavily booked prices on offer will be higher) will drive prices up.
AerLingus and Flybe lost a packet on LGW since EI entered the route Oct 2012. EI stuck it out and to their credit they waited, success on the LGW route should be a good result for the long term outlook at BHD for them.