A couple of people have mentioned I haven't said how I fitted/wired up my super cheap reversing camera...
So...
There is a hole in the middle of the boot with a rubber grommet in it.
Pull the grommet into the car and you will see a "tail" hanging down on the outside of the car, covered in black electrical tape, which is covering some rubber tubing to make the tale containing the cables.
I carefully cut all that off and pushed the extension lead and power socket through it.
Then once the camera is in place (stuffing the connectors in the hole first) you get under the car can hopefully can see the four cables. Connect them up
I then pulled back some of the slack into the boot (possibly a bad idea, because if it doesn't work, I am going to have to take the bumper off to check the connections!) and taped up the grommet again with the rubber tubing and new electrical tape.
For the power, I took the negative to a bolt in the boot. Then for the positive, I put a tiny slit in the light green wire in the grommet on the passenger side behind the reversing light, put her in reverse and used a power tester to check if there was power to it when the car was in reverse.
Then I used a cable clip thingy to attach the power to the green cable.
(There are two, a light green and a dark green, I will check which I used later today
Running the video lead to the HU is pretty easy. I took the cable to the passengers side and followed the amp cables, then the aerial lead from the aerial.
Saying all that, I am yet to connect it up to the HU, so it might all be crap as I haven't got it working yet!