'Constitutional and Administrative Law' by Bradley and Ewing is what I would call basic textbook reading. Use this book to get an understanding of the basic law, and then supplement it with a good dose of essay-reading and other books (see, for example, that essential collection of public law essays 'The Changing Constitution' by Jowell and Oliver and 'Public law' by Adam Tomkins)
Part of the difficulty is that the textbook follows a certain pattern which might differ from the one used by your own professor during lectures. As such you will have to try and find order in the book. While it is often very thorough, there are some topics that are so essential for a student to grasp that I would say the book needs more information on it. For example, the 'written but codified' status of the constitution is a given essay-question on every exam and could thus use a more thorough analysis (cf. Public Law by Adam Tomkins) and the impact of human rights on judicial review receives barely two pages of text while on my exam there was a question along the lines of "discuss the effect of human rights on judicial review".
I was honoured to have professor Ewing as my professor of public law, and found that his lectures on police powers, human rights and the terrorism acts were much more informative (and much more useful from a problem-solving/essay-writing point-of-view) than his textbook.
It is a shame that the humour, vigour and passion for the subject shown by professor Ewing during his lectures did not translate as clearly to his textbook.
Overall I would strongly advise students to read this to get an understanding of the basic questions in public law, and to then go out and visit the library. To a student this might sound a bit off-putting, but public law is very much a political subject and there are thus a variety of opinions on the different topics, it is thus often a joy to read the essays and papers.