Derek Bourgeois (b. 1941) is a British composer of music for all sorts of ensembles large and small.  He has written over 300 compositions, including 72 symphonies.  Serenade is a relatively early work (opus 22, 1965).  Says the composer:

Derek Bourgeois wrote this Serenade for his own wedding, to be played by the organist as the guests left the ceremony. Not wishing to allow them the luxury of proceeding in an orderly 2/4, the composer wrote the work in 11/8, and in case anyone felt too comfortable, he changed it to 13/8 in the middle! The work has now been released in a number of different orchestrations of the original version for organ.

Here is the band version (created by the composer in 1980) in performance:

And, for context, here’s the organ original:

Derek Bourgeois has his own website with a lot of information about himself and his music.