Ian McEwan is one of the best modern British authors I've ever read anything from. I recommend you start with Atonement.
There's JK Rowling, who is one of the top international authors... I'm sure you've heard of her stuff.. ;D
Then there's CS Lewis (noted for the Narnia series), JRR Tolkien (noted for the Lord of the Rings trilogy), Lewis Carroll (noted for Alice in Wonderland)...