Unfortunately I have to agree with previous posts. However, a path can be declared a right of way if it can be shown that it has enjoyed free access for a period of (I think) 15 years. If you can show your local authority evidence of unrestricted access by vehicles (anybody's vehicles) for this period then they will add it to their definitve rights of way map!
As to your subsidiary question, this is more clear cut!
As long as there no parking restrictions on the road (e.g. yellow lines, permit-only parking, within 50 metres of a roundabout etc. etc) a taxed vehicle can be parked anywhere on the public highway. The fact that it is outside someone's house is irrelevant! It would even be OK for you block his driveway if his car wasn't on it! (If it was you would be causing an obstruction!) Tell all your friends/family to park in front of his house. If he rants and raves in the street report it to the police as public nuisance!