But! I do have a book of the month for you all. The Thirty-Nine Steps by John Buchan. It's only about 100 pages, so it's an easy read. The book is a bit Holmesian in the way it was written, so if you like Conan Doyle, you'll probably like this. It's a pre-WWI spy novel, with the main character, Richard Hannay, finding himself in possession of a notebook of secrets and the London police on his case for a murder he didn't commit. It's the first of five novels featuring Hannay, though this is the only one I've read. One of my favorite things from the Wikipedia page is that Buchan described it as a "shocker"--which is "an adventure where the events of the story are unlikely and the reader is only just able to believe that they really happened."
Alfred Hitchcock made a movie in the 30s based on this book, though rather loosely I understand (I haven't seen it). The BBC came out with another version in 2008, which I did see, with Rupert Penry Jones as Hannay, and they added a romantic angle to it (not in the book, but who doesn't like a little romance, eh?).
If you're looking for a good British spy novel, I would suggest this over something like Tinker, Tailor, Soldier, Spy, which I found very hard to get through.