MV -
You say that a walkway at Bristol would be very long, but have you visited Luton in the last few years? There is now a walkway from the East side of the new terminal round to stand 1, on the western edge of the old main apron. Signs suggest passengers allow 15 minutes (!) for the walk, and there are no travellators/moving walkways. I don't know how far it is, or how it compares with distances at Bristol, but you walk past the equivalent of a dozen or so nose-in parking stands.
I don't believe Luton required planning permission, and it was constructed during Mr Kehoe's reign....