It will probably be different for other places but at my university, the maths in the first semester were pretty much just a recap of A-level stuff. It was only in January that we started going into stuff I hadn't done before. That said, it's a fairly quick recap so you might struggle a bit if it's the first time you're seeing the material.
If you're willing to work a bit harder to keep up and are able to learn some stuff over the summer, I think you'd be ok going straight into first year.