GB seem to be in an interesting position these days. Their future is of course largely out of their hands and in the hands of their paymaster Willie Walsh of BA.
Yes the "low costs" must be cutting their margins a bit, but on the other hand they are quite low cost themselves, and as a bonus have BA's marketing to supply them with customers.
The big question for GB is whether BA would like to buy them out (not a cat's chance in hell) or whether BA decide to stay or go at Gatwick. If they go - and it seems there is a 50/50 chance of that happening over the next few years, then GB will no doubt be ideally placed to pick up the pieces and profit nicely from them. However if BA decide to make a go of it at Gatwick you can expect them to reclaim routes back off GB, raise the price of doing business for GB and I wouldn't want to be on the wrong side of the fence when that happened.