Even if you now try and push the tractor The low efficiency worm will jamup and not allow it to move.no not quite correct they will still roll down hill or can be towed off ,not too aggressively mind, but they do still move.The Fordson F and N models didn't have brakes as such. They only had an oil immersed multi-plate clutch and one pedal. The cunning design used a worm gear final drive. Worm gears are very inefficient (less than 50%). Any final drive gear system with less than 50% efficiency will not transmit power from the wheels back to the gearbox. Thus when the clutch pedal is depressed and disconnects drive from the engine, the tractor glides to a halt due to the worm drive efficiency problem. Even if you try and now push the tractor, the low efficiency worm drive "jam-up" will not allow it to move. No brakes to wear out. There is a small loop to keep the clutch pedal down if you want to stop temporarily without disengaging a gear. The penalty is the gross 50% loss of power to the drawbar (the 50% loss of power appears as very hot transmission oil), but the system served the Fordson well for over quarter a century until the E27 Major was introduced with a high efficiency spur gear final drive (but needed separate brakes).
The simple to drive one pedal system meant that the Land Army girls quickly became expert Fordson drivers in both world wars playing an important part in keeping Britain fed. Ford Detroit shipped 6000 Fordsons to the UK in 1917/18 and Ford Dagenham supplied many thousands in WW2.