I don't think for one minute they even considered LTN and LGW was a definite no considering the 83 weekly flights they have announced at STN.
C'mon guys, putting aside the fact that I do know for sure that they considered other London airports, how can you possibly believe that a canny and sucessful company as Jet2 would make an investment of this scale without first thoroughly evaluating ALL the possible options, no self respecting Board would accept such a proposition.
I will confess to having no knowledge if STN was their preffered or just their only option in the end, that was just a poke at the local fanboi's for lulz