I didn't have any witnesses when two cars from my household were both bumped into and damaged both our cars - on seperate occasions leaving red and blue scrape marks down our cars. Co-incidentally Warwickshire Stagecoach buses had just been re-routed up our road and would not admit liability cause we didn't have a witness though the damage caused was blindingly obvious who done it.
See for yourself - I'm soooo disgusted with them I have built a website in there honour!!
Stagecoach Bus
They've changed the route now but left carnage behind for us to pay for!!!