I can't help directly with the tune, but I can tell you that the song has been recorded by Roy Bailey (with Stalking Horses: "Never Leave A Story Unsung", FUSE records CFCD 398; and with Band of Hope: Rhythm & Reds, Musikfolk).  Robb Johnson himself has released it on "Margaret Thatcher: My Part in Her Downfall" (Irregular Records IRR042).  There are also plans for a songbook; see Moose Music's rather disastrous website:  Moose Music UK

Malcolm