I listened again yesterday to Ricky Gervais and his Guide to the Arts. He did, in fact mention the piece of music. It is:
Five Variants on 'Dives and Lazarus'
As a collector of English folk tunes, Vaughan Williams was struck by the a tune he discovered in 1893 in a copy of English Country Songs called Dives and Lazarus. Over the next 40 years he found different versions of the same tune, sometimes under different names, such as The Star of the County Down as it was known in Ulster.
And so the Five Variants
are not a set of variations in the conventional sense, but
“reminiscences of various versions” as Vaughan Williams describes them.
They demonstrate his ability to incorporate simple folk melodies into
almost symphonic creations.