As railway-ers we tend to think of Listers as lightweight 2' gauge industrial locos, but I'll bet they sold more of these. I'm not sure how big the engine is, but it can't be more than 10hp. Pre-fork lifts, depots would have a couple of these chugging around - possibly with a trailer or two. I seem to remember them in the sorting office carrying mailbags.
This preserved example shot at Tenterden station a decade ago.
P.S. Have just noted that Mr. Campbell has refered to these as 'factory tugs'. See link to right for his rail version in the building.