I agree, jumping into the bear pit that is Scotland / London domestics without codeshare / interlining arrangements up against BA that will be aggressively pricing when eventually the world reopens would be total folly. Of course the slots don't have to be used for the rotes specified, but I am struggling to work out which routes Flybe2 could possibly make work from LHR, except NQY or EXT, even perhaps LPL but that would be extremely iffy given the rail links to the capital.
There are probably many "safer" routes from the UK regions to mainland Europe that I would have thought they would be considering before LHR.