Hiya, I have a foward facing childs seat in the back of my Discovery 1 (n/s), I had to remove the plastic stop lug in the belt to allow the clip more movement down the belt and trim the bottom corner of the childs seat to sit on the wheel arch.
When I had the rear facing childs seat (one you carry from baby age) I bought the seat base that fits in the car and the childs seat just pops on top and clips in place securing it to the base. It was fitting with the centre lap belt.
If you go to mothercare they will tell you what seat fits in what cars!
Not alot by the way!