An appallingly dull book on an interesting and important subject. The title should be 'the Penguin guide to correct English: 1940'. Whilst everything the author says is correct, he isn't moving with the times and bemoans the evolution of the English language.
Not only that, but the whole approach of the book is incredibly boring and seems to be based purely around bad examples of the incorrect use of the English language and showing how they could be improved.
If you want a guide to plain English then look elsewhere: this won't help you