I strongly recommend this reader friendly pocket size reference book for students studying sociolinguistics. The book not only provides ample examples on colloquial British English, but also once more stresses the fact that descriptive grammar is as equally important as prescriptive grammar. The book is published by Lonely Planet and the details can be accessed directly from the following link:
Tarah!
Is it possible to find it in ebook format?
This title appears to not be available in digital PDF format, but why not check Lonely Planet website directly?