Naturalist Mike Dilger explores Europe's longest chalk reef off the Norfolk coast. The North Sea may have a reputation as grey and murky, but this rare and important marine habitat lies within easy reach of the beaches of North Norfolk. Large areas of the North Sea remain undiscovered and the full extent of the reef was only revealed last year when local divers mapped its 20-mile length. This makes it the longest in Europe, maybe the world. A colourful underwater world complete with valleys and arches and teeming with life, it's got marine experts very excited. Proposals put forward to the Government would make the reef part of a new marine conservation zone. But some conservationists say the plans don't go far enough to safeguard its future.