The London Post Office deep level tunnel scheme was also accompanied by the construction of a new set of remotely controlled floodgates for the London underground. Both projects took until 1957-58 to complete, by which time the advent of the Soviet H bomb had made the protection they afforded a little futile. In the earlier A bomb era, however, a Hiroshima or Nagasaki type of weapon exploding at ground level would perhaps have left the deep level tunnel system intact; this at least was the hope. A postwar Home Office manual on civil defence protection suggested that 'shelters constructed to provide protection (against standard five hundred or one thousand lb bombs) ... should normally be capable of being strengthened to provide protection against atomic attack.'

The digging of the Post Office London tunnels began in 1951, after some fifteen months of urgent planning. The first phase of the scheme was to construct the underground telephone exchange, Kingsway, in the citadel and shelter tunnels which had been built below the Chancery Lane tube station. At the same time, another shaft was dug in Whitehall Gardens, a street no longer in use immediately to the west of the present Ministry of Defence Headquarters. The MOD offices, then known as the New Government Offices, were still being completed, on top of two wartime citadels, Montague House south and north. This shaft was used for extending the Whitehall tunnel network both around Whitehall, and to link it directly to the Holborn tunnels and Kingsway telephone exchange. A map of the current system Figure 16 (p. 25) shows how this was done, by driving a shaft from Holborn through Covent Garden to link up with the Whitehall tunnel at Trafalgar Square.

By 1954, a basic network was near completion. The Whitehall network of bomb proof tunnels and citadels was linked to the major trunk exchanges at Faraday (Citadel), Kingsway, 'Trunk Control North' at Judd Street near Kings Cross, and the Museum telephone exchange (site of the present Post Office Tower).

Kingsway itself went into service in October 1954. With a permanent staff of one hundred and fifty, it connected over thirteen thousand long distance lines. It had its own 1.5 mw Generator, and oil supplies for six weeks' operation (22,000 gallons) stored in the tunnels. All lines to and from the exchange ran via the deep level tunnels, and through them to the underground or Post Office railways. Four extra tunnels were dug under buildings to the south of High Holborn to accommodate automatic switching equipment. By the time Kingsway was in full operation, it was the major long distance exchange in the British telephone system, switching between 1.5 and 2 million calls a week. It has its own artesian well for water, food supplies, canteen and emergency accommodation.

The secrecy of the new government project did not last long - a report of the 'Secret network of tunnels' appeared on the front page of the Daily Express in September 1951. The article accurately listed four tunnels being dug for Kingsway. The four - two in Fumival Street, one behind Staple Inn Court, and others opposite Southampton Buildings in Holborn - are all still in use to provide foods lifts, ventilation, oil inlets and exhaust outlets for the underground exchange, leaving the area littered with a remarkable, but discreet, collection of clandestine technical workings well blended into their surroundings. The main entrance (plate 32) remains unmarked and unremarkable, as though it were a goods entrance for adjacent shops and offices.

The Express reported some official Post Office comments on the tunnels: 'a depth of one hundred feet underground gives the maximum atom blast and radiation protection in the central London area.'

The Post Office claimed that they were: 'only concerned to a certain extent, because telephone lines would be required in the tunnels ... I am not allowed to say much more. It is work in connection with defence.' Which was more than a slight misrepresentation of the Post Office's involvement.

The government was rather more concerned when a second article appeared three days later describing the second shaft being dug to build more tunnels under Whitehall. At 10.15 the same day, a secret meeting was called by the Cabinet Office, attended by two Commanders from the Security Service (MI5), together with Post Office and Ministry of Works officials. They discussed issuing a D Notice, or a Confidential warning to editors, or merely a suitably misleading press release from the Post Office. The problem was particularly severe because the public might get the (correct) idea that the government was building deep shelters in Whitehall for itself whilst refusing the public any such protection. The minutes of the secret committee, known only as MISC 379 observed: 'It would be embarrassing to the Government if the public got the impression that deep shelters were being constructed. Either the public would think that the Government were out to protect their own skins and those of their immediate servants; or the public would assume that the shelters were intended for public use in time of war and would be disappointed when they found they were not.'

After experiences of government attitudes to public deep shelters in the Second World War, the 'Public' might have a more cynical reaction. The minutes added: 'The Home Office in particular would be embarrassed because Government policy generally was that no significant shelter construction could be undertaken at present because of lack of resources.'

It was ever thus. There was also the problem that an enemy, knowing details of where 'the British government was constructing underground accommodation' could allocate 'his scientists ... to constructing bombs especially designed to penetrate so far.' The prudent enemy might have imagined that such accommodation would be under Whitehall anyway. An MI5 investigation of the journalist and his sources came up with no leads beyond a report that he had had drinks in a pub with a number of those working on the Kingsway site. Severe security precautions were therefore instituted to try and prevent leakage about another phase of the project known as 'Post Office Scheme 3245'. This involved the construction of another shaft in Horseguards Parade and the Mall (for which the Trooping the Colour ceremony had to be moved). The Scheme started in October 1951, and was to involve some four to five hundred workmen for several years.

A second meeting of MISC 397 noted: 'Details of the existing network of Post Office tunnels, with which the proposed new tunnels would be linked, had been published together with explanatory diagrams soon after the war. It would therefore be possible to guess with some accuracy at the possible direction of the new tunnels, even though they would not run (from A to B). But the information which it was most important to safeguard was the use to which some portions of these tunnels would be put, and this would not be obvious until the equipment engineers got to work ... an astute journalist had only to ask one or two questions of different workmen to learn enough to piece a fairly accurate picture of the tunneling system.'

Only about a third of these tunnels were in fact to contain Post Office equipment, although 'this would lend authenticity to the official version of the purpose of the tunnels'. The Post Office prepared a press release, which falsely stated that the whole project was just a set of cable tunnels: The shafts and tunnels being driven in several parts of London are being constructed for the Post Office. Experience has demonstrated the advantage of using deep tunnels for Post Office cables in congested street areas... A tunnel of this type was provided along Wood Street as long ago as 1925, and some years later another was constructed along Holborn.

A final sentence referred to the need to protect 'vital communications' in the 'present defence situation' and the installation of 'terminal equipment associated with the cables'.

Nothing further was published about the Whitehall tunnels through an article suggesting that the government was indeed building itself an atom bomb proof citadel appeared in- the Daily Worker on 8 September 1951. In 1980, I was personally able to explore much of the system of Post Office cable tunnels and see what in fact had been constructed. There has been much speculation about just what lay 'beneath the city streets', as Peter Laurie's book put it. My explorations were not authorised by the Post Office, who nevertheless took no action when they were reported (New Statesman, 1&25 December 1980) - save to suggest, untruthfully, that perhaps my trips had all taken place in a photographic studio.

There are more than ten miles of the basic cable tunnels and they are impressive. But, apart from the sections under the Whitehall area, they house only cables - with occasional large chambers in the vicinity of shafts or elsewhere, for 'repeater' boxes, amplifiers, and other interconnections. There are toilets and rest rooms, but no underground switchrooms or dormitories (except Kingsway). The Post Office network, as such, is only for the cables. Access to the network is via shafts inside the adjacent exchanges, or via a very few shafts coming into subways below ordinary streets. Such subways are at Bethnal Green, Waterloo, the Mall and Maida Vale. Anyone going into the system is warned by notices that they should hold a 'deep level pass'.

Large lifts at the major exchanges can carry drums of cables and other equipment down the necessary eighty to one hundred feet. At some sites, small, specially-built electric trucks wait to move the equipment around, plugged into their battery chargers. There is no permanent presence in the tunnels, only the day shift of staff installing new cables and maintaining the network. It is quiet and carefully ventilated; at some seven or eight points, there are frequent rumbles as tube trains pass some distance overhead. The Post Office tunnels are the deepest of any of London's underground networks.

The use of the deep level network has eventually proved a cost effective way of connecting tables where tunnels already existed. In the 1960s and 1970s, the Post Office made significant additions to the system, both in London and in Manchester. Some of the tunnels have been filled to capacity, such as the original wartime tunnel along Holborn, and other tunnels have provided new routes between exchanges. A general view of the tunnels is on p. 108. It was not possible to explore south of Trafalgar Square, and consequently an exact contemporary description of the Whitehall part of the system after the war cannot be given. A function of the Whitehall shafts may simply have been to remove spoil as the Post Office tunnels went north from Trafalgar Square.