Like framer, I too when on the spanners, did full power ground runs - at LGW. Starting from the east end, taxing to the run up bay at the west end. Getting back sometimes involved entering the main runway, unlocking the flight controls, adding power and taxing back, quickly. The need for a pilot to do it was never mentioned in those days.
The golden rule on any power runs, wherever you do them is, in the event of sudden aircraft movements, shut the throttle immediately and stand on the brakes. It seems that did not happen at CPH.
Just hope the guy in the tractor recovers.