Assuming GCSE as a starting point (National Curriculum Level 7/8), this A-Level mathematics text provides transitional material in the early chapters for students from a variety of mathematical backgrounds, and caters for a wide spread of ability. It contains the core for A-Level mathematics as outlined in all examination board syllabuses, and additional coverage is included to cater for the pure maths content of A-Level mathematics courses combining pure maths with mechanics / statistics / decision (discrete) maths, and the first "half" of A-Level pure mathematics.
It's an adequate introduction to the mathematics topics needed to be covered for my college course. I found the book to be clear in its explanations and didn't have much trouble understanding it. There are better books sure, but this one's ok too.