I had high hopes for this book but was left a little disappointed.
There was lots of stuff in here that I had forgotten but most of it I will surely forget again because I'm not too interested. The bits I was interesting in (maths and science) I found that I did know (because I read sciencey books anyway) and it felt a bit lightweight in that area.
The book mostly covers early secondary school topics and touches on some of the basics from 'O' level (I guess that's GCSE now).
Overall, I think it is worth a read and it does deliver what it tries to. My problem is that my expectations were unrealistic (but that's not the author's fault).