Ah, good old Moggy Cattermole ... "Piece of Cake" is an excellent book!
You might also be interested to know that Derek Robinson (a former RAF FIghter Plotter) has written on this very subject: http://www.amazon.co.uk/Invasion-19...d_bbs_2?ie=UTF8&s=books&qid=1195942591&sr=8-2
His conclusion: that even had the RAF been wiped out during the BoB, and the Germans had had Air Superiority, such was the strength of the RN at the time that the Germans would not have been able to get over the channel.
IIRC it was all to do with the fact that there were no proper invasion craft. German troops would have had to be towed across the Channel in flat bottomed barges, at the stately speed of around 4 knots. It would have taken them 14 hours or so to cross, meaning that part of the journey would have been in daylight. A few Destroyers cutting thorugh the invasion fleet would have swamped most of the barges on their way over.
Robinson put this all in 'A Piece of Cake' with a conversion between the US woman reporter and some of the member of Hornet Sqn in a pub (The Fleet Air Arm pilot on the squadron, tells everybody that the chances of a successful German invasion are about zero, due to the fact that the RN destroyer force would sink most of the barges just by their wake and the air battle is in fact irrelevant). Robinson also puts into the mix CH3’s comments that the outcome of the air battle is relevant, like in the fact that somebody has to beat the Germans at something just to show the world that the Germans were not invincible (Like the USA government for starters, which Fighter Command successfully did). As for the German's Sea Lion was a Bluff, without doubt, Overlord took over a year to plan.