A traffic conundrum

Imagine a small town road with speed bumps near the primary school. Just after the speed bumps end there is a left turn that goes behind a few houses and leads to a medical centre and day care centre. At the top of this road there are two lanes but this soon narrows to a single lane that enters the medical centre car park.

Always at the top of this little road, right next to the junction, there are cars parked on the left hand side. Usually two and sometimes three. This means in effect that the entire road is single track. So someone turning into the smaller road has to use the 'wrong' side of the road.

Now imagine that someone dropping off a passenger at one of the afore-mentioned houses has reversed into the small road without parking properly so the entire road is blocked for someone turning left from the main road. This car cannot be seen until the car turning off the main road has got round the parked cars that are too near the junction.

My question is: who has right of way? Should the driver off the main road reverse back into the main road because they are on the 'wrong' side of the road. Or should the road-blocker reverse out of the way?

Note: the 'main' road is often essentially single track too because of parked cars.