An overly harsh review which raises some points that need clarification.
The reviewer has completely missed the point of the book; this is not designed to be another 'Beaches, fields, streets and hills' (also by the same author). It is a mistake to pick up 'Defended England' and its companion volume 'The Battlefields that nearly were' and expect them to be a continuation of 'Beaches, fields, streets and hills'. The latter was an archaeologist's report aimed at the archaeology community; the depth of research and analysis, however, also appealed to a wider audience.
Look at 'Defended England' for what it is; a narrative text designed to introduce the layman to the subject by telling the story (yes - the story) of the author's research and travels through the landscape of 1940; a fascinating insight that deserves to be examined on this basis, and not compared with something it was never intended to be.
From the information that accompanies the "sadly drawn" maps it would seem that they have been sketched from wartime Ordnance Survey maps. Three points on this:
1. Sketch maps are what the archaeologist often uses in the field, so you're getting a flavour of the subject.
2. The maps are also the sort of quality that one regularly sees in the WW2 archives drawn by those who actually built the defences.
3. Copyright costs prohibit the use of colourful printed maps in every chapter; the author's sketch maps are designed to show the basic layout of the defences in relation to the landscape (a job they do well); they're not intended to be works of art.
With regard to incorrect information and ommissions, this is inevitable when you look at the sheer size and scope of the author's research and walking many parts of the country that were probably unfamiliar. Having said that, he was using the Defence of Britain database and quite a few local contacts in the areas he describes. You could contact the publisher with a list of corrections/additions - they should pass it on to the author. Or why not start your own research project as I've done in my area - I can highly recommend it!