I am going to assume the expansion will be in England
Firstly it could be expansion of services from an existing 'base' (i.e. MAN or LBA) or it could be the launch of a base at an existing destination (i.e. NCL). I think its pretty safe to say any expansion wont involve NEMA (near to BHX) or LPL
If its a new destination they will expand at, here are the contenders
BLK - Could be some potential for domestic services, particularly Belfast City (they used to serve the route in Jersey/British European days on Summer Saturdays). However Jet 2 (and also ZB/FR) have Spanish routes covered and French regional services would probably work better from MAN
DSA - Definite potential for domestic and French Regional services, and the airport could do with some more low cost flights with TOM's growth being pretty much non-existant as far a scheduled flights go. However, might affect development of the airlines LBA base
HUY - Potential for a 'NWI' style operation with domestic flights to ABZ, EDI, GLA, BHD, JER, SOU, EXT and international services to CDG, Chambery (winter) and Spain. However, smaller catchment area compared to DSA
MME - Quite unlikely in my opinion, but BHD, SOU and EXT routes could be possibiities
I suppose if the expansion is for this winter there will be announcement in the next couple of months, if its for next year I would expect something in the Autumn