Dollis Hill's secret wartime 'citadel'

Far below the streets of a north London suburb a labyrinth of concrete chambers lay unseen, partly flooded and derelict. Hardly anyone knew it was there; the only way in was through an anonymous door that was always locked and discreetly guarded.

Older residents remembered a major construction project in the Thirties, but whatever was known about the mysterious works below Brook Road in Dollis Hill had been forgotten long ago. Until now.

In this improbable setting, surrounded by neat semi-detached homes, the British government hid one of the best-kept secrets of the Second World War. The underground chambers were duplicate Cabinet War Rooms, built as a last refuge for wartime leaders in the event of German bombers forcing them to abandon their bunker in Whitehall.

The complex was known by Winston Churchill's closest staff as his "citadel" because it was completely bombproof, unlike the famous command centre in Westminster that has been preserved as a museum and is open to the public.

Those rooms near the old war ministry and Downing Street were strengthened as the conflict approached but the government and military knew they would not withstand a direct hit. So it was decided to create an impregnable duplicate, codenamed Paddock, at Dollis Hill.

If the Battle of Britain had been lost, this is the place from which Churchill would have given his orders. Paddock's location - and very existence - was so secret he referred to it in his memoirs only as being "near Hampstead".

The citadel may have remained a secret except for the assiduous researches of historians and, a few years ago, a decision to build on the site. A housing association, Network, secured planning permission to build 37 homes on top of Paddock - but there was a snag. The Ministry of Defence wanted access first.

Network building surveyor Robbin Williams said: "They wanted to clear out any possibly sensitive material."

Ministry contractors took maps, files and numerous pieces of equipment but much remains and Network and its partner organisation Innesfree decided to open the rooms to the public once a year. The first visitors will be allowed in today but the Evening Standard was given an exclusive preview tour.

It was an eerie experience. Some parts of the Paddock site have not been touched since the war, although water seepage and damp have attacked every surface. Fungus covers the walls and ceilings, stalactites cling to the concrete slabs overhead and mouldy fronds hang from the original ventilation ducts, light fittings and doorways encased in steel.

The place reeks of drama. What happened in those dank chambers? Who went there? Thanks to the efforts of the late historian Ken Valentine, many of these questions can now be answered.

Mr Valentine, a retired civil servant, discovered documents that showed even King George VI was not told exactly where Paddock was located. When building began in the late Thirties the project was known as the Emergency War Headquarters. The idea was that it would be one of four bombproof underground citadels; the others would be used by the three military services.

When the war began in September 1939 it was thought officials and government employees would be moved to the western half of England, out of German bomber range. But with the fall of France in June 1940 and the Luftwaffe's ability to launch attacks from there, this plan was abandoned. Paddock became a vital part of the strategists' planning.

The bunker was designed for the entire war cabinet with 200 staff. It was 40 feet below ground with an outer covering of steel-reinforced concrete three and a half feet thick and a small, deep chamber covered by two layers of concrete six feet thick separated by loose sand to absorb the shocks of repeated bombing. Paddock was considered capable of withstanding any weapon used at that time.

Churchill hated it. There were no flushing lavatories and he had to use a fire bucket as an ashtray for his cigars. A room with a bed and a few pieces of furniture was provided for him but two flats were converted for his use in a nearby building, Neville's Court, when bombers were not a threat.

Paddock contained a broadcasting studio and, according to one account, the actor David Niven had been provided with facilities to send out a radio message impersonating Churchill if the wartime prime minister was forced to escape London.

Churchill's secretary, John Colville, wrote of the day a two-car party, which included Churchill ' s wife Clementine and son Randolph, inspected "the flats where we should live". Mr Valentine was convinced these were the apartments in Neville's Court, which had just been requisitioned by the government. Colville also noted that they inspected "the deep underground rooms safe from the biggest bomb".

Some of the things they may have seen on that day are still there. There is a kitchen with two deep sinks and the remains of cabinets; rooms with expansive tables and glazed partitions that were probably used to set up maps, constantly updated to follow the progress of the war. Original light fittings remain and single bulbs dangle from the old fabric-covered flex.

The generator that provided electricity is virtually intact, as is much of the other machinery including pumps to raise fresh water from a deep well.

The old switchboard frame stands in one room and a few broken filing cabinets have been left in another.

A small room where the bed and furniture were found - marked with the number 13 - is believed to have been Churchill's bedroom, at least by Mr Williams.

"I love to think of him being down here at the height of the Blitz," he said. "You can imagine him walking along these corridors, people running around with secret messages; the tension and anxiety as they watched the war."

In fact, Churchill used Paddock only once. After the war he wrote: "On September 29 (1940) I prescribed a dress rehearsal so that everybody should know what to do if it got too hot. I think it important that Paddock should be broken in."

A cabinet meeting was held, he recorded, "far from the light of day" and the occasion was celebrated with a "vivacious luncheon".

Later in the war, Churchill's place of last resort became the bomb shelter of a building in Great Peter Street, Westminster, and Paddock became redundant, slowly overtaken by the decaying damp.

One person who saw it as it was, before the Ministry of Defence cleared it out, was Rupert Allason, the former Conservative MP.

In his alter ego of Nigel West, the thriller and spy writer, Mr Allason came across records in 1981 that led him to Paddock's location.

He said: "I persuaded the security man to let me go down and have a look. It was amazing. There was a lot of telephone equipment, large maps and a place that had clearly been used as a war room.

"It was all in fairly good condition but obviously hadn't been used for years."

With the first visitors arriving today, Paddock has again found a role.