It seems that when Walton's score was thrown out and Ron Goodwin commissioned instead, Lawrence Olivier threatened to have his name removed from the credits unless his friend, Walton's, was reinstated - a compromise was reached by using the the Battle in the Skies sequence as described by WUB.
Got to get up to Shuttleworth again - next evening show is the eve of the London Brighton bike ride I think (14th) so I can't make that one as I have to be up at Pre-Sparrow fart... soon, I promise!