Tony Banks, the culture, media and sports minister, issued the order on the Hanover, a mail ship, to prevent any "unauthorised interference because of the historical and archaeological importance".
The decision is likely to spark a row as the treasure hunter, Colin Martin, has spent upwards of pounds 1m in trying to find the site of the packet which sank off Cornwall in 1763 laden with gold, diamonds and cannons worth pounds 50m at today's prices. As recently as Thursday, his salvage company recovered 14 cannons from the ship, which lies on the seabed off Perranporth.
Last night, Mr Martin was taking legal advice and vowing to continue. He condemned the department's decision as "disgusting" because the company had been acting in a "perfectly correct manner".
"We're carrying on exactly as before because the ship is in danger. We removed the guns, so there's nothing to keep it there and it's going to end up smashed to pieces if there's a storm," he said
Earlier this year, the Post Office applied to get the wreck designated because it claimed ownership. It said the Hanover was part of the packet service which was the forerunner of the modern Post Office. But no order was granted.
However, a Department of Culture archaeological diving unit has been observing the salvage operations. The department decided to step in yesterday because the site was considered to be under "immediate threat".
To proceed, Mr Martin, 35, and his company, Hydrasalve, will have to apply for a diving licence. These may be granted to commercial divers but they have to satisfy the department they have a proper plan and expert advice.
The department spokeswoman said: "We need to be satisfied that the method of operation is acceptable and is not going to damage the archaeology of the site. The ship is a historic ship from the 18th century and had a valuable cargo."
A Post Office spokeswoman said it had not lobbied the department to obtain the order. But she added: "We are relieved that the wreck and its contents can now be surveyed and possibly salvaged in line with best practice. It will enable this part of our heritage - both national and Post Office - to be properly studied."Reuse content