There are different sorts of parodies;

The Billy Connolly "D.I.V.O.R.C.E" parody takes the mickey out of the original and deservedly because it is so naff.

The "Green Fields of France" to me is different as it takes the mickey out of drunks in bars and the fact that a well known song is often appallingly treated.

Most of the times Les Barker's parodies are not aimed at the original song, but using a well known and familiar song to highlight a humorous angle on something - the "Nolans and Elton John" doesn't really make any cooment on "Lowlands" but the humour comes across by the twist in the application of the lyrics and tune.