Honestly, I don't know that much about foundation years, not as much as some of the teachers on here. The little I know is because I considered it as an alternative route to uni. I know it's supposed to be for those with either low level 3 grades or the wrong level 3 subjects. That means they teach everybody level 3 content. They wouldn't start level 4 content for people who haven't even learned the subject at level 3. Some people in that foundation year won't have Physics or Maths A Levels like you.
As for the progression, it depends on the uni and how much space they have. From what I've heard, the higher the uni's reputation, the tougher it will be to progress because a lot of the students doing a foundation year there will be those capable of getting A's and A*'s. The pass mark will be high. For some unis, you could be fighting for a pre-determined, limited number of spaces. You can check the uni's website to see what their individual progression policies are. I believe most unis guarantee a place as long as you get a certain grade at the end of the year.