Just stumbled on this thread and thought I'd chip in, even if it is an old one. The words as I remember them are pretty close to Dave's version:

Come all you gallant drivers, wherever you may be,
Whether you drive a Euclid or a fifty-four RB,
Keep your hands upon the levers, cut and fill a steady load;
Now you're goin' nice and steady boy, a-ploughing of the road.

We have dug a hundred airfields through the snow and wind and rain,
Built atomic power staions, more dams than I can name.
We have cut through rock and swampland, moved mountains by the load;
Now you're goin' nice and steady boy, a-ploughing of the road.

And when your digging days are over and you've loaded your last ton,
When your Cat is broken up for scrap and your RB-ten won't run,
When you've had your last stamp on your card, and you've reached your last abode,
For a long time after there'll be people travellin' on your road.