Don't forget the various 'stop' lines. Its actually quite easy to find a bunker if you spend a day walking around the countryside in the south. Still around 200 of them that could be made operational quite easily if need be.
The entire basis for German tactics required the ability to use combined arms in highly fluid maneuver warfare. Its hard to see how any of that would have been applicable in south England. Even if things had gone as well as Crete and they had had total air dominance. They essentially would have been up against a very well prepared defence in depth, which is the one tactic which is effective against a blitzkrieg.
Hell, they would have had to take a major port before any significant amount of their armour could be brought into play. By which time the home squadrons of the Royal navy are blasting their way into the channel. Even if a magical fairy gave the Germans an aircraft carrier group and the RAF had nothing left to put into the sky, it would have been next to impossible to establish both an effective beachhead and an effective supply route across the channel.
Part of the reason why British history is the way it is, is that its extremely hard to establish an effective beach head in Britain, irregardless of the navy (which obviously in this scenario is extremely important). the last time it was successfully done was in 1688 largely because William of Orange was invited in. the previous time before that, well, the Vikings were still about and were directly responsible for the Normans being able to land uncontested at all.