Now as we've decided invasion by air and tunnel isn't going to work, we need more lateral thinking here.
So I consulted the whales, and they came up with the following suggestion, courtsesy of them watching Braniac on TV.
If you pour custard powder into water, it produces a substance with the odd property that, although a liquid, you can walk across it. So we just need to put two barrages down in the channel to form a closed area (thats the Kreigsmarines job), dump enough custard powder (courtesy of the Luftwaffe) into it, and the Wermacht can just march across into England.
Simples!