'I think we're all intrigued by what goes on behind those high barbed-wire fences, 'says Wayne Cocroft.
'I've been very lucky. In the last 10 years I've seen so many secret places.'
Before its amalgamation with English Heritage, Cocroft was a 'field recorder' for the Royal Commission on the Historic Monuments of England (RCHME); his title now is 'investigator'.
He spent much of the 1990s studying the remains of the gunpowder and military explosives industries, and his book based on that research, Dangerous Energy, has just been published. Cocroft has gone on to explore the intriguing structures, often subterranean, built during the Cold War. If you want to know what has been happening behind our backs for years, he is the man to ask.
Cocroft had early inklings of his eventual career.'I was one of those peculiar children who liked clambering around castles - they sparked my imagination. I wanted to become an archaeologist.' He went on to study archaeology at Cardiff University and then 'worked on the excavation circuit for four or five years', with short-term contracts that included a spell of 'rescue archaeology' at Winchester when the M3 was under construction, and projects abroad - excavating a village site in Turkey, for instance, which was threatened by a dam.
At the RCHME, Cocroft first tackled 'a very mixed bag of work'.This ranged from a survey of hill forts in Staffordshire to an investigation of Gertrude Jekyll's garden for her own house, Lutyens' Munstead Wood in Surrey, where the commission's team discovered a medieval packhorse track at the heart of Jekyll's planting scheme. It was with the break-up of the Ministry of Defence estate at the start of the 1990s, with many major sites slated for disposal, that Cocroft's specialisation began.
Dangerous Energy is an immensely detailed, sober historical survey - but a heading early in the text strikes another note.It simply says 'Wow!'.The reference is to a turningpoint in Cocroft's life, his first visit to the 71ha Waltham Abbey Royal Gunpowder Mills on the north-east fringe of London (AJ 5.6.97).
'We were amazed by what we found, ' he says.'This place had been a totally secret research establishment.We hacked our way through the undergrowth and made discovery after discovery.But some left us completely bewildered.'
Fortunately, as the site had only recently become redundant, many of its records were still intact, and they were vital in deciphering these mysterious remains. The necessary complement to Cocroft's research in the field is just such a study of documentary evidence - a chronological sequence of maps showing the evolution of a site, perhaps, or a sheaf of government papers in the Public Records Office at Kew.
As a result of Cocroft and his colleagues' investigation, two thirds of the Waltham Abbey site is now a scheduled ancient monument, with 21 listed buildings among its 300 or more structures. There are, for example, the Grade I-listed Incorporating Mills of 1861 - 'architecturally the grandest gunpowder mills in Britain' - and a strange series of earthmounded chambers for the manufacture of nitroglycerine, still half-hidden among the trees.'What we immediately perceived here was a whole landscape, ' says Cocroft, 'and we didn't want its preservation to be piecemeal.'
He adds: 'We see ourselves as landscape archaeologists.
These kinds of remains, sometimes undergoing several changes of use, linked together in various patterns of dependency, threaded through by waterways or other lines of supply, can best be understood from that perspective.'
Such once-working landscapes recur in Dangerous Energy, above all in its aerial photographs, where the profusion of earth-mounded features - necessary to contain explosions - may evoke momentarily a prehistoric site.They are the focus too of Cocroft's current studies.
'When you consider Britain in the twentieth century, you're looking at a very militarised landscape - especially during the Cold War, ' he says.There are all sorts of structures to examine:
emergency government headquarters, anti-aircraft defences, research establishments and missile stores.The nuclear bunker in the photograph is just around the corner from Cocroft's office in Cambridge and he would like to put it forward for listing.'If this isn't Brutalist I don't know what is, ' he comments, 'but it's very photogenic.'
Two sites dominate his conversation: Spadeadam in Cumbria, where the British Blue Streak missile was tested at the end of the 1950s; and Greenham Common in Berkshire, the American Cruise missile base in the 1980s (when, thanks to Thatcher and Reagan, the Cold War turned glacial again).
With its giant concrete test stands built on remote boggy land, Spadeadam involved 'terrific feats of engineering', while the massive missile-storage silos at Greenham should, Cocroft thinks, be proposed as a scheduled ancient monument.
Cocroft is now completing his text for the Cold War followup to Dangerous Energy, which should appear in 2002.
Reflecting on its contents, he says approvingly: 'There are vernacular-style brick radar stations from the 1950s but essentially this is an architecture of reinforced concrete, earth and steel.'You don't doubt for a moment where Cocroft stands.
These stark silos and bunkers mean as much to him as any childhood castle.
Dangerous Energy (£45) is available from English Heritage Postal Sales.Tel 01536 533500, fax 01536 533501