The English Channel and the North Sea.
The North Sea is between Britain and Europe.
The English Channel is the body of water which is located between Great Britain and Europe and is a part of the Atlantic Ocean,
The English Channel and the North Sea.
English channel
The English Channel and the North Sea.
Great Britain and northern Europe east to the Caspian Sea
The main geographic defence was the body of water between mainland Europe and Great Britain. This body of water was controlled by the greatest navy on the planet.
The North Sea and the English Channel.
In terms of geography, Greece and Great Britain are far apart. Greece occupies what can be called the southeast section of Europe and the major body of water it is close to is the Mediterranean Sea. On the other hand, Great Britain can be said to be located in the northwest section of Europe, with the Atlantic Ocean as the largest body of water bordering it.
Great Britain (not Briten!) has the English Channel to its South and the North Sea to its East.
A map of Europe when the British Isles were connected to mainland Europe is included in the link below. You can see the outline of both Great Britain and Ireland as they are today as well. The green obviously indicates land while the blue indicates water.
The Irish Sea and St Georges Channel and the North Channel and even the Celtic Sea could be said to be the bodies of water that separate the two islands.