it's funny you should say that, cos after applying as much considerable pressure as i dared using an open-end 12mm spanner i could feel the nut would round off, so i hacksawed the old strut off so i could use a 12mm socket, a really good fit too, but it rounded off anyway.
Toyota must of employed a gorilla in the factory wrenching them on at 1000 Nm.
I'll try again tomorrow using a pair of vice-grips, they look a big big for the job, just hope the jaws can fit in the gap.
For the time-being i now have a one-strut tailgate...