I took it out of the shed and the handle dropped off. I secured the handle and plugged it in and it went zzzzZZZZZzzzz but nothing moved so I unplugged it and looked at the underneath and realised that it was pretty well rusted into place.
I managed to move the blades a bit, trapping my thumb in the process, but also in the process realised they are about as sharp as a plank of wood. So I think I need a new lawnmower.
If only I'd realised this sooner. We could have raced it last week!