The score here is perhaps a little harsh, as this is a good book, but there is a reason for it. For those that have read the 'Short Introduction To' series of books, you will know that these books are normally quite objective, and provide a good source of information for those who wish to learn about a subject, or are students of it.
Not so with this book. It makes a good stab at being objective and informative, especially at the beginning, but as the book goes on it becomes more and more of the author's view.
The author, Tony Wright, is a Labour politician, and this comes through very much in the writing. Here is someone who knows what really goes on, but for me I didn't want to know what really goes on, I wanted a dispassionate, informative account of what British Politics theoretically is. This is too one-sided, too involved in the subject.
It is certainly not a memoir, so does have use, and the writing is light and easy. If you don't want a 'textbook' on British Politics, it might be useful for you. If you have read other books, and want a more personal look at the subject, it will definitely be a good read. But as a starter book, which most of these 'Short Introductions' are, this isn't the best.