Remains of a ship that sank to the seabed off the Suffolk coast around 500 years ago have been categorised as being “at risk” in an updated list of the nation’s heritage treasures published today.

Experts revealed that the wreck of the 16th Century vessel on the Dunwich Bank has been plundered by thieves who last year stole one of its bronze guns.

Historic England’s Heritage At Risk Register gives an annual snapshot of the condition of some of the country’s most important historic buildings, sites, monuments and places.

In Suffolk, the wreck is the latest addition to the list, while Grade II* listed Kersey Mill, built in 1810, has been removed following major structural repairs aided by an £80,000 Historic England grant.

The shipwreck site is marked on sea charts and sits around 50ft down.

It was once suggested to be a casualty of the Battle of Sole Bay 1672, but is now believed to be the remains of an armed merchant vessel from the 1500s or possibly a rare example of an early military transport vessel.

Historic England said the site had been placed on the “at risk” register due the discovery of the theft of a gun from the site in the summer of 2015.

Stuart Bacon, a marine archaeologist and director of the Suffolk Underwater Studies unit, discovered the wreck in 1994 and recovered one of its bronze guns, which was displayed in his shop at Orford for many years and is now exhibited at the Dunwich Museum.

Mr Bacon said while the wreck may be at risk there was no action being taken to reduce the risk or protect it.

He said: “It’s a very hostile site and because of the amount of sediment in the water you have to work in the pitch dark by touch and sound – you would need to be a quite accomplished North Sea diver to go down.

“The ship’s guns should really be brought ashore so they can be cared for – not left to degrade in the sea and be at risk of being stolen. I asked eight or ten times for an excavation license and was refused.”

In Essex, the listed 12th Century Church of St Mary at Ovington, near Braintree, has been added to the list because it is in a “very bad condition suffering from subsidence and cracking in the north and south walls”.

However, the 85ft high Naze Tower, built in 1720 by Trinity House as a navigational tower for seafarers, has been removed after a £168,349 grant from Historic England allowed removal of inappropriate sand and cement mortar and embedded steels, and structural repairs.