A bit of a search and it appears he was probably Des Farmer:
1975: SWINGALONGAMAX (Victoria Palace)
Max Bygraves, Bobby Crush, Denise Keene & Happy, Rogers & Starr, Judy Allen, Peter Durkin, Lee Gibson, Adele Neatrour, David Brenchley, Des Farmer, Carol & Ann, John Melainey, Roger Sutton; devised and directed by Lionel Blair [16pp, 5.5x8.8; biography of Max Bygraves, full details and credits for each items, 10 photographs of the cast etc.; VG] £4
There's also a program on Ebay where his name appears once for one of the songs.