The British Museum website has steadily uploaded images of prints and drawings from its collections including the Ronald Searle material. I was able to visit the museum and look through the original drawings of 'The Rake's progress' in 2009 but time was limited and I couldn't request to see everything. However the website turns up this fascinating artifact-
Searle's rough draft sketchbook in which he compiled the sketches with the finished printed cartoons. It's insightful to see how Searle altered the compositions between the rough and the final image.
(Click on an image to go through them full screen)