It seems clear to me that easyJet's hand will be forced in the case of the London Gatwick slots for flights to Belfast, and I suggest City, in order to keep Ryanair out of the local market.
Ryanair have hit their domestic operations at STN already with entry onto GLA and EDI, but to have Ryanair coming onto more routes at LGW is the last thing easyJet would want.
I'd put my money easyJet going after this at this stage....