Heya Kvitty,
I currently do the Foundation Physics and Astronomy course at Sussex, I didn't apply to it but a 3 year bsc, they changed it as I didn't get the required a levels.
The course itself is basically a more focused version of A levels that you do in a year. I like the course, I have learn't much more than I could of at college as I am being taught by masters in their subject who know what is important and what isn't for your degree and are more about knowledge then trying to get pass a qualification.
If you are going to get a levels equal to or above the standard, and you feel you are ready for the degree, you can skip the foundation year but otherwise, its a good way to make sure your 100% up to speed!
If you have any more questions do ask!