It started as a top-secret military site, built in the midst of the cold war, but has since fallen to a state of disrepair.

Now, the UK's first independent nuclear deterrent, in Suffolk, will be restored and repaired with a series of conservation works.

For the Barnham Nuclear Bomb Store, a nine-acre site on the Gorse Industrial Estate between Elveden and Barnham, near Thetford, is one of the latest additions to the English Heritage at risk register.

This includes 6,000 buildings and historic sites at risk of being lost, including monuments, archaeological sites, battlefields, shipwrecks, places of worship, conservation areas and landscapes in England which are under threat from neglect, decay and damage.

Keith Eldred, who bought the Suffolk site from the Ministry of Defence for �20,000 in 1966, initially to grow mushrooms to sell to Woolworths, is working with English Heritage to restore the area.

'This was the most top-secret place in the country,' he said. 'My wife nearly passed out when I said I'd bought it.'

Built between 1953 and 1959, the bomb store was created for the maintenance of the Blue Danube, Britain's first free-falling nuclear weapon to be stockpiled.

Today, the site, which has been subject to vandalism and moisture over the years, is a fascinating snapshot of a top-secret world that once was.

It includes 57 'kiosks' which housed the nuclear components, although only about 16 were ever occupied, bomb-storage units, five watchtowers and is a scheduled ancient monument with three grade II* and two grade II listed buildings on site.

Four of the towers will now be restored – with one left to demonstrate slow decay over time – and the kiosks and perimeter concrete wall repaired. Scrub will be cleared, a water tank restored and a testing store preserved.

This will be funded with a �80,000 grant from English Heritage – which will cover approximately 80pc of the costs while the remaining 20pc will be funded by Mr Eldred.

Inspector of monuments for English Heritage, John Ette, said the organisation had been working with Mr Eldred for some time, and expected the remainder of the work to be completed in about a year.

'There's nothing particularly unique about some of these buildings and even the observation towers themselves aren't particularly unique but what's important here is probably what the site housed and how significant it was as Britain's first nuclear deterrent,' he said.

'It was all about security and secrecy. They were out of the way and down on the heathland and they wouldn't be bothered.'

Most of the restoration work will be carried out on site, which is a scheduled ancient monument and which is also partly used as an industrial estate.

Any work to 'beneficial' buildings – those which could fetch Mr Eldred rent, for example – will be funded by the owner.

Historic buildings architect for English Heritage, Ian Harper, said: 'It's about caring for each individual component and aspect in a way which will allow its knowledge and history to be seen in the future.'

While sites on the at risk list include those with the highest levels of protection, Grade I and II* listing, across the country, English Heritage also this year announced a programme to assess England's 345,000 Grade II listed buildings.

It will fund between nine and 15 pilot surveys with local authorities and other groups to find out which such structures are at risk.

One already in danger is the site of the remains of the Church of St Andrew, in Bircham, which has become overgrown and is in an advanced state of decay. There are no current plans for its repair or re-use.

Another building known to be at risk is 33 Bethel Street in Norwich, an 18th century town house which has been vacant for the past decade and is deteriorating. There are no active plans for its reuse and the building stands next to the former Bethel Hospital which is listed at Grade II*.

Mr Ette added: 'Grade II listed buildings are the local authority's responsibility to look after so we tended to do the Grade I and scheduled monuments but we felt there was a bit of a gap and they're still an important part of the national story so we felt to neglect them was completely wrong.'