I've never used Purivol but it's probably like all other anti-spot (acne as they say in the US) products.
I've always found that:
1.) It helps a little in stopping spots, especially smaller ones and generally clears up your face a little removing black heads etc
2.) You'll still get spots anyway though, including the MASSIVE ones. Sorry, that's life.
3.) You'll end up getting dried out skin in the winter if you use them religiously.
I'm afraid that you just have to grow out of it. So no cure I'm afraid but at least it might help a little. To be honest, the confidence boost probably does more for your appearence than the actual anti-spot ingredients