I read this book when it was first published because it named someone I had known well for many years.
The background was this: Josef Frolik defected from Czechoslovakia, and published a book about his alleged activities as a spy. It was difficult to verify the details because, with one exception (the tale about a planned honey trap involving Edward Heath) Frolik did not name names. Chapman Pincher obtained tape recordings of interviews given by Frolik, and re-used his anecdotes, this time including the identities of the British people allegedly involved.
Frolik appears to have had a vivid imagination. A BBC Radio 4 programme ("The Heath Caper", broadcast on 25 June 2012) investigated the alleged trap to trick Edward Heath, and found little to substantiate it. As regards the person I knew who was named by Chapman Pincher but not by Frolik, the anecdote about him was demonstrably untrue, and he was able to prove that he was never in the circumstances postulated by Frolik.
I don't know how much of the detail of Chapman Pincher's book is verifiably correct, but the snippets I know about from personal experience are the product of Frolik's imagination. I recommend taking this book with a Pincher of salt!