When EZY and FR enter an airport they don't usually operate 1 route, they will expand from the airport, especially in places such as Spain where tourism is extremely high. GIB is just too small for that sort of operation, but do not rule out a LC carrier into the airport.
There are many out there such as LS, AB, Wizzair and SkyEurope to name afew. If we were to name a UK route I would have to say TOM from MAN. Two UK airports are already served by BA (GB) and ZB along with BA and IB on the MAD route, so there is a possibility of the resurection of MAN at the airport after ZB cancelled the route.