Philip Chambers is a writer almost next nothing is known of. He was born in 1936, is possibly dead by now, wrote six Sexton Blake stories in the early sixties and nothing else. I've skimmed through his Blake story Bullets to Bagdad (1960) in which a secret organization is planning to take over the government in Iraq and take their oil supplies. In the story Blake's boss is and old man called Craille. He's the leader of the British counter-intelligence organization, as secret as the criminal organization in the book.
Here are some of Chambers's Sexton Blake covers. Pretty good ones, too, but I don't know the illustrator. There's a signature in Keep It Secret!, it seems it says "S. Barany".