As you say Dave there is NO DESIGN SPEED but they MUST adhere to the design parameters laid down and some Councils do not do this. About two years ago Hillingdon Council I think was fined thousands for a dangerous structure under Health & Safety regs and ordered to pay a couple of thousand pounds compensation to a guy that had a "super car" (Lambo or something) damaged by a road calming hump that was way over height and had the wrong approach angle.
We win sometimes but not often like Leslie Ash and the recent NHS payout for getting sick in Hospital. Problem my mum died due to getting a Hospital infection so couldn't sue.
Hugh