Sorry I might be bit thick here but, if it will take 20 mins to tie down the load, for a 400m journey, why not drive it, possibly not road going would it take much to get it road going? you say digger, is it tracked? or Wheels? if tracked will need H class group on driving licence, but I am sure there are many tracked diggers etc going across roads, and used in public places that the drivers have not got the licence for, now the rules have recently been changed?
He doesn't want a metal floor to avoid this problem which he doesn't currently have..
Not sure what the council would say about 16 tons skewing round on a road.. plus it wouldn't be road registered? ?