MMario - the opening lines as written by Keith go:
No man who's a drinker takes ale from a pin
For there is too little good stuff there within
rather than the entry in DT which is very weak in comparison.

I gather that it was about the first song that Keith wrote and that for many years he let people think that it was traditional. If you want to find more of his wonderful songs, try and get hold of his songbook "Picking Sooty Blackberries" - it was sadly published postumously, but has quite a lot of info on the background to each song.