The Making of the English Working Class
by E.P. Thompson
Considered a definitive text for many years this book is dense, academically rigorous and utterly superb.
I needed a dictionary, wikipedia and a notebook to get myself through the first quarter but once up to speed with the authors style and concepts, it was as compelling a read as I have ever had.
This book has the advantage of being widely respected across all academic and historical fields in a manner which some of the other books I have read are not.
The Many-Headed Hydra
by Peter Linebaugh and Marcus Rediker
This book gives much food for thought, bringing a fresh perspective to number of themes such as slavery and pirates which help put English peasant struggles of the time in a wider context.
Whilst I would highly recommend it, I would also advise with some caution as the scholarship is not as widely respected as it might be.
This review from the Guardian does a good job and it worth a look – http://www.theguardian.com/books/2001/jan/27/historybooks