Is there not a 5th option - to use the area for housing and create an alternative source of income?
"Conveniently located for Luton's shopping and employment centres, good access to the M1, main-line station close by, no danger of flooding ........" - I can almost imagine the estate agents' hype already!
I have no idea how this would compare with income from the airport concession, but it would surely be more profitable than converting it for sheep and dairy farming.