it is illegal to park a car on the pavement (even mounted) where not allowed. if you were to scrape it, it would be very easy to claim that 'but for the fact that the driver had not parked illegally, you would not have scraped his/her car'. the pavement is designed for your use, not a car's and you are not obliged to use the road if the pavement is blocked. it would simply be an accident if you were to scrape the car as you had no intent to do so. the car is blocking your right of way, a call to the police would fix the problem very quickly. the car owner is parking his car at his own risk.