The cover blurb announces this as "an astounding work of myth busting", and indeed myth-busting is the primary focus of the book. Unfortunately, the first myth is one made completely of straw: that Britain "fought alone". Some say that was from June 1940 (the Fall of France) to June 1941 (the Invasion of the Soviet Union); some say for the whole war (at least in some form of "alone"). There was a lot said about this when I was in London in 1995, and a debate on Wikipedia a decade later. In any case, author David Edgerton huffs and puffs at this house of straw.
The next is made of sticks. Some historians have alleged that Britain had no realistic hope of defeating Germany and that the war was pure folly. I blame David Irving but anyway Edgerton lays out the case that Britain was competitive with Germany, and that its leadership was confident of victory throughout the war. There's some very interesting comparisons with German equipment, although Edgerton overreaches a bit here. We all know that British tanks were no match for the Tigers and Panthers, and carrier aircraft were a failing, mitigated by the adaptation of land designs like the Supermarine Seafire and the purchase of equipment from the United States. The editors who know off the top of their head how many inches wide a Panther was may have the hoodwink warning lights go on a few times.
The most interesting argument is about the role of technology. Britain envisaged a technological war (attributing victory and defeat alike to superior technology) and in the end largely made it into one. Edgerton points out that Britain might have done just as well without Frank Whittle's jet engine, Barnes Wallis's bouncing bomb or the sticky bomb, but there is also Donald Bailey's Bailey bridge, and I think the book is a bit hard on the hedgehog, which the USS England used to sink six subs in as many days in May 1944. The extent to which this British perspective of warfare influenced American ideas is something that calls out for more exploration.
The book has much to say about the British war economy, but if you're really interested in the subject, I would recommend Margaret Gowing and Keith Hancock's British War Economy.