AFAIK, Eastern Airways were the
only Airline to offer a guaranteed backup a/c. If BA did, I cannot remember one at Manch
I seem to recall that originally BA did say that the shuttles would have back-up a/c & crews at each end ...
but in practice ...
I think the "back up" applied only to the LHR end, unless anyone knows better ?
But I do recall from my days at LHR that even that didn't always apply.
Every Christmas the shuttles (and particularly the BFS) ran out of a/c and/or crew by early afternoon .. with long queues of pax building up .. and many, many pax gurmbling about "where were there back-up's promised".