Driving home tonight and whilst doing 70mph (I think!) my speedometer just went mad and starting registering 120mph, then 80mph, then 60mph and then back to 120mph. It carried on doing this all the way home, even at lower speeds (turning into my drive it registered I was doing 60mph, but I could hardly have been doing more than 10mph). What has gone wrong and will it cost a lot to fix it?
Car: Renault Megane 1.6 Alize 1998 (S Reg) - if any off that helps. Perhaps it was just enough to say Renault.