I was wheeling it through the tip car park, and it didn't rattle or jitter, just sounded near silent and rolled perfectly smoothly. It was when I went to lift it into the car that I worked out why - it is made of bloody thick alloy and weighs a tonne.
Sounds like Victa's 1970s answer to their high arch rear catcher Victa pro from the 80s and 90s with the super beefed up cast alloy chassis.