While this has been gone over in length on this board and others, the short answer is the invasion would most likely have been a disaster for the Germans.
The British had 30 destroyers and about 200 smaller vessels positoned to counter the invasion. Larger ships, up to a battleship in size, could have made the invasion crossing area in less than 24 hours.
The invasion fleet itself would have taken somewhere between 48 and 96 hours to cross and another 72+ hours to actually complete the landing. The biggest gun among the escorting vessels was a 4" with the vast majority of the escorts being converted fishing trawlers with nothing bigger than a 37mm AA gun. When you add the marginal stability of many of the vessels crossing (including about 1000 8 to 10 man outboard motorboats suitable for fishing on your favorite placid lake ) and the total lack of sailing experiance of most of the crews, you get a recipe for massive destruction and loss of life among the invasion fleet.