What geographical feature separated the United Kingdom from the rest of Europe

The geographical feature that separates the United Kingdom from the rest of Europe is the North Sea.

The North Sea is the water body that lies between the United Kingdom and the continental part of Europe. With France and Benelux being just on the south of it, and the Scandinavian Peninsula on the east. We can also include the English Channel, as it is separating part of the north of France and the south of the United Kingdom.

This was not always the case, and the territory of the United Kingdom was relatively recently (geologically speaking) connected by land with the rest of Europe through a land that is now bellow water called Doggerland, and that was until the end of the last ice age.