I think that the government should shut the M25 for 1 day and allow the public to drive round the orbital in timed runs (both ways). I'd pay £50 to do it, imagine the revenue it would raise? You could start and finish at the Dartford tunnel or bridge.
Who else would fancy ragging thier motor round the motorway in such a way?
Or what other roads could you suggest doing it on, perhaps reopen the Birmingham superprix road course of the early 90s?