Rob Spray believes the reef needs to protected against fishing activity and cable access.

A diver who helped discover the sprawling size of the world’s longest chalk reef has warned more needs to be done to protect it, 10 years after it was designated a Marine Conservation Zone (MCZ).

The Cromer Shoal Chalk Beds, dubbed Great Britain’s Barrier Reef, external, date back more than 100 million years and stretch 20 miles (32km) along the Norfolk coast from Happisburgh to Weybourne.

But diver Rob Spray, who uncovered the reef’s size with Dawn Watson, said the “conservation zone has brought nothing in the way of protection”.