I think BE sounds like the best contender
Another turbo prop operation as the ATR is very similar to the Dash with regards to operating cost, capacity etc
Something tells me they had an arrangement with BE quite some years back when the Q400s when just coming in
They would probs get a good deal with prices from SEN and would put them back into the London market but with significantly lower costs
they know demand on EDI and BFS where good for EZY the only problem was the A319 was too big, so a prop could be perfect size
They already use operate ATR for flybe Nordic so are very aware of the aircraft
My odds are on BE