As much as i like Jet2, everyone on here seems to think they're Easyjet Killers, which i doubt...to a point
The main benefit from Easyjet at BFS/LGW is their economies of scale, the sheer number of based a/c at both bases mean that if Jet2 were to have any major impact, they'd need to go in just as hard as they did with STN, which they won't have the available aircraft or slots in destinations to make it work
That said, Jet2 do seem to have the better product with their holidays offering and their consumer awards, and the South of England might not be as price driven as their Northern heartlands might be.
Regardless, until Jet2 put in a new order, they won't have the aircraft to make it work, so Easyjet (and everyone else) can breath easier for now