Over the course of a few centuries many great powers attempted to invade the British Isles with some failing and others succeeding. The primary reason Britain was able to retain it's independence from continental European powers such as France and Germany was the fact that it was an island separated by a 200 km channel.
However in 1942 Channel Dash a German task force was able to sneak through the English channel in broad daylight. My question is, was invading Britain that difficult? The English Channel was frankly that not that wide and the British would need time to prep their fleets to intercept an invasion force.
While more can certainly be said, the relevant section of my user profile contains several previous answers where I discuss the difficulties any attempted German invasion of Britain would have faced, and how they were likely insurmountable.