My advice would be don't take it if you don't need it, it's not easy especially if you have a crap teacher like I did in my two years of college.
If you want me to be completely honest, I don't think A-level physics is as hard as A-level chemistry, I found chemistry a lot harder mainly because there was so much material and formulas/equations/mechanisms to remember. The material for physics at A-level is really less but it's the understanding that's the difficult bit. If you understand all the concepts, you can do well in exams, without any exam paper practice. But with chemistry you need to practice a lot of exam papers.
My physics teacher and chemistry teachers at a-level were so bad, I practically self-taught myself both subjects. I came out with an E in chemistry and a C in physics.
Anyways, I'm just talking from my experience, it's just an opinion. My friends who are good at chemistry hate physics and my friends who are good at physics hate chemistry!