Two 2nd hand buys from Amazon resulted in two great reads, The Springing of George Blake by Sean Bourke and The Blake Escape by Michael Randle and Pat Pottle. I read the books when they were first published, Bourkes in 1970 and Randles and Pottles in 1990.
The two books will hold you to the finish, both books are amazing tales of Blakes escape from Wormwood Scrubs Prison and the twists and turns on the road to East Berlin.