Have finally got round to checking the lyrics (in under five years!) and find nobody else has deposited them in the Mudcat or DT, so here's the version that Hamish Imlach sings on 'Sonny's Dream' (1985):

THE REPROBATE'S LAMENT
(lyrics Bill Hill / Tune trad)- from the singing of Hamish Imlach

          Oh dear, what can the matter be
          I've got problems with my anatomy
          Since I've discovered some pounds extra fat on me
          I'm scared tae stand on the scales

I'm no a fella that's partial tae joggin'
Aerobics or cycling or similar slogging
Carbo-unit counting or calorie logging
I'm scared tae stand on the scales
I once knew a man who was aye in a hurry
Tae put on a tracksuit, his health made him worry
He ran intae the road, got hit by a lorry
Now he can't stand on the scales

The health freaks all think I'm a bit of a nutter
My digestive tract is an absolute clutter
Bagged down with chips and white bread and fresh butter
I'm scared tae stand on the scales
O' eatin' junk food I got intae the habit
For I couldn't stomach the diet of a rabbit
I tie my shoelaces, finish up wobbit
I'm scared tae stand on the scales

Tae Scarsdale's and F-plan's I'm no a subscriber
I can't stand the hamster food people go fibre
I'm a consistent big overimbiber
I'm scared tae stand on the scales
My dissolute life on my health puts a levy
For I must confess I'm quite fond of the bevvy
Never too much, eight or nine pints o' heavy
And I'm scared tae stand on the scales

          Final chorus:
          Oh dear, what can the matter be
          I've got problems with my anatomy
          Since I've discovered some tons extra fat on me
          My God I've broken the scales

[1985:] I am fat (not plump, chubby or cuddly) and lazy (not laid back, relaxed or cool) and happy with it! (Notes Hamish Imlach, 'Sonny's Dream')

The tune is 'Johnny's Sae Lang at the Fair', and it was the thread on that song which brought me back to this one. Sorry Nick, but then you already know dealing with me requires a lot of patience ...