Disclaimer: I know that this site doesn't provide proper legal advice. I just wanted to get an answer relating to something that has just happened, I'm not planning on pocketing the advice and taking it to court it's more a case of how worried I should be.

Returning from work this afternoon I turn around onto my driveway and crunch... there is a car parked in it and I've driven into the back of the car.

1. The driveway is my private property and I did not give permission for the owner of the car to park there
2. I do not know who the owner of the car is.
3. The driveway is accessed via an alleyway and the entrance is partially obscured by a wall immediately next the driveway. I was approaching from the side where the wall obscures the view of the driveway entrance.
4. If this was a turning on a public highway I would hold my hands up and say that I wasn't driving with enough care as I came around the corner, I wasn't speeding, I was maybe doing 5mph but I did just swing my car around the wall onto the drive, not expecting there to be a car in my path.
5. This happened in broad daylight.
6. I am aware that a car being parked on your driveway doesn't automatcally absolve you of any damage you do to it but the only references I could find online were to: cars parked blocking, rather than actually on, your driveway (i.e still on the public highway) and people doing deliberate damage to cars parked on their property.
7. While a lack of visibility came up as a possible mitigating circumstance in cases of accidents this was still referring to cars blocking your driveway and used darkness as an example of lack of visibility which may result in the driver having reduced liability.

The damage to my car appears to be a small leak to the screenwash tank, but come to think of it I was feeling before this that I never seemed to have as much screenwash as I thought, so perhaps the leak was always there and I'm only just noticing it. Other than that the only visible sign of an impact is the amount of paint from their car that is now on my bumper.

Somehow their car came off a fair bit worse, I guess because it was the corner of my bumper versus the centre of theirs, but they now have quite a lot of cracks across the entire length of their bumper (assuming this is new damage that I caused).

I have moved my car, not purposefully to flee the scene of the accident, but because I had to park it somewhere, I couldn't just leave it in the alley and so have parked it on the street round the corner from the alleyway. Nevertheless it does have the effect that when they do return from wherever they went (I leave near the city centre so I'm guessing they went shopping but it's possible they were visiting a neighbour) there will be no sign of how the damage was done. However they know whose parking space they parked in as my flat number is painted on the driveway in big letters so there's a chance they'll come knocking on my door claiming I am liable for the damage.

I guess I just want to know how worried I should be that I'm going to end up with a hefty bill, points on my licence and a hike to my insurance premiums.