Former FCO/MI6 Secure Communications Sites of Buckinghamshire 2 of 3 – Creslow

Location: Creslow, Buckinghamshire, UK

Date of visit: July 2023

Type: Former FCO/MI6 Secure Communications Site

The posts in the Buckinghamshire series are periodically updated when new information comes to light. This page was most recently updated on 30/03/24.

Isolated even by Buckinghamshire standards, the former communications centre at Creslow is accessed by a long single track and sits at the rear of farm buildings at the top of a hill hidden behind a thick veil of trees.

Its history appears to run in parallel with that of the sister site at Gawcott, starting life during WWII then being used by the intelligence services throughout the Cold War before being sold into private ownership in the 90s.

Creslow was established as a radio communications facility for Section VII (Communications) of MI6 back in 1944, it would have facilitated the sending of messages to MI6 agents in occupied Europe.

As is confirmed below, Creslow was linked to the Section VII headquarters at Whaddon Hall, Buckinghamshire. Ultra intelligence would be sent to agents in the field from sites such as Creslow via Whaddon Hall. It is understood the Creslow site was likely created in direct response to Section VII commander Brigadier Sir Richard Gambier-Parry’s drive to improve MI6’s communications links with agents abroad.

At the start of the war, radio communications were sent from the tower of the Bletchley Park manor house, this transmitter was later disassembled and moved to Whaddon Hall and then supplemented with other transmitter facilities such as Creslow which is less than 20 miles to the south.

The Creslow site pictured just after WWII¹

As with the other sites in this series, what happened at Creslow between the end of WWII and the early 90s is shrouded in a cloak of secrecy and wears a hat of mystery.

A limited insight is given in its entry in the Historical Dictionary of British Intelligence as follows –

‘Creslow Manor. A powerful radio transmitter built in 1944 at Creslow Manor in Buckinghamshire provided Whaddon Hall with an additional link overseas. After World War II, it remained in operation for the Diplomatic Wireless Service until 1993′

The declared operation of the Creslow site by the Diplomatic Wireless Service (DWS) doesn’t give a great deal away – whilst there’s no dispute that the DWS existed, exactly what it did and who it did it for are vaguer.

An advert from 1967 placed in The Shortwave Radio Magazine seeking Radio Technicians to work at DWS sites including Creslow and Gawcott²

Now known as the Foreign, Commonwealth and Development Office (FCDO), the official mission of the DWS was to provide secure channels of communication to the UK Government and Foreign Office, the intelligence services would fall within this customer base too. Up until the end of the Cold War the existence and scope of the work conducted by the DWS was secret.

Documents held by the National Archives offer a useful history of the DWS and also help confirm its ties with the intelligence agencies.

A history included as part of a review of the DWS in the early 70s states that the DWS was formed in 1947 ‘by the transfer of a quasi-military communications organisation to the Foreign Office’. Within the remit of the DWS was the provision of a number of secure lines of communication to British embassies abroad including telegrams, secure speech, bags and broadcasting, with ‘intelligence support’ also being an important component of the DWS mission.

As described in Top Secret correspondence from 1948, ‘DWS has, as its main task, to provide a world-wide tactical communication network for the Foreign Service and for the combined Secret Services’. It continues, ‘the essence of this communications network is that it provides direct point-to-point communications between the Foreign Office and HM representatives at foreign posts, and, at the same time, between the HQ of the combined Secret Services and their foreign representatives’.

Further correspondence from 1951 provides evidence of MI5’s stake in the operation of the Creslow site. In a secret memo written by ‘H Fenton Esq’ from MI5, a description of the function of the Creslow site is given in reply to enquiries from the military about security provision to DWS locations around the country. MI5 state ‘Creslow is the point to point transmitting station which again forms the centre of the whole DWS network and is keyed by remote control from Hanslope’.

As part of the same chain of correspondence from 1951, the Foreign Office sent a Top Secret list of DWS stations to the military as part of a ‘key point categorisation’ exercise designed to establish the importance of the sites to the DWS and accordingly, the level of security that they should be afforded.

On this list, Creslow Manor is described as a ‘DWS Wireless Transmitting Station. The function of the station is separate from that of the Station at Kingstanding. Neither could replace the service in the event of damage to one or the other’. Also included on this list is the DWS HQ at Hanslope Park which is given as a ‘receiving station’, Kingstanding in Sussex which was home to the Aspidistra transmitter, a factory in Borehamwood used to manufacture cryptographic machines, the former Political Warfare Executive HQ at Whaddon Hall and finally Poundon which is listed as an emergency site ‘held on care and maintenance’.

Documents in the National Archives offer a history of the DWS and confirm its links to the British intelligence agencies

Nowadays the FCDO is (slightly) more open about its work, in recent years it was involved in the construction of the Remote Radar Head at Brizlee Wood in Northumberland, an air defence radar station the plan for which has a similar appearance to the Creslow site –

Not a dissimilar layout to Creslow although very different purpose – the Remote Radar Head at Brizlee Wood, another station claimed publicly by the FCDO³

Based at Hanslope Park, the FCDO were contacted to see if there was anything they were able to contribute by way of a history or maybe even archive photos of the three sites in this series but had declined to do so saying only that the sites had been used by the government⁴.

As stated in the first blog of this series, Creslow is mentioned in the UK Intelligence And Security Report August 2003 with the following entry under a list of previous FCO sites –

‘Creslow – Buckinghamshire (Numbers Station- enormous site rebuilt 1993-97, closed by 1998)’

Quite how this document came to be on the internet is unclear – it is unusually candid and appears to have been leaked but there’s nothing to suggest it’s inaccurate, even if it’s not clear for which audience it was originally intended for.

Photos of the Creslow site taken at some point during the Cold War show the presence of an antenna farm and plant buildings including a similar semi-circular transmitter hall similar to that seen at Gawcott. The antennas at the site appear to be log-periodic types –

class= — Creslow Park prior to the rebuilding of the site in the late 80s⁵

Creslow Park prior to the rebuilding of the site in the late 80s⁵

A plan of the Creslow site is held in the National Archives produced as part of a survey in June 1987 showing the layout of the buildings shown in the above photographs prior to redevelopment of the transmitter hall.

The buildings listed on these plans as ‘office stores & workshops’ and ‘riggers store’ are still visible today, cleared were the transmitter hall and also engine house, further stores and garages. The schematic shows a mass of cables once extended from the east and south of the main building and out to the numerous transmitters that would have stood around the site.

A plan of the Creslow site from the National Archives show the layout of the old transmitter hall and ancillary buildings

At the end of the 1980s it is known that the Creslow site was cleared and the building that can be seen today erected, complete with its own high voltage electricity supply and later fibre optic links. A wire mesh was built into the walls of the new building to form a Faraday cage, blocking any electromagnetic leakage of sensitive information.

When in operation, the fields adjoining the transmitter station would have been covered in a variety of different transmitters and aerials, just as they were at Gawcott.

Given its declared association with the Foreign Office, the site was well suited to maintain communications with British embassies around the world, asking them if they had sufficient stocks of Ferrero Rocher chocolates and dispatching more as required.

Construction of the current buildings on the Creslow site at the end of the 1980s⁶

Detail in the above photos provides a useful opportunity to discuss in a little more detail what connectivity at sites such as Creslow and Gawcott may have looked like, along with how and by who the messages they were built to send were composed.

Transmitter sites tend to be selected according to geographical criteria, elevated ground is the preference as the higher the transmitter, the further its signal will travel. This is the case for all three sites in this series. The same criteria rarely suits the positioning of the studios that produce the audio or video content hence a studio transmitter link (STL) is required – commonly a terrestrial microwave link or a wire/fibre optic connection.

During WWII, the STL between the PWE studio at Milton Bryan and the transmitters at Gawcott and elsewhere was initially a motorcycle courier physically delivering a record. Later a dedicated wired connection was provided to directly link the studios to the Aspidistra transmitter in Sussex.

Photos from Creslow and Gawcott indicate the presence of microwave links, these would have been required because the whilst the broadcasts from the stations were sent from their transmitters, they were almost certainly written and encoded elsewhere.

As microwave transmitters shoot in a direct line of site to a corresponding receiver, the receiver can be located by drawing a straight line from the direction in which the transmitter is pointed. The receiving station station will be somewhere along this line, the higher the transmitter the further the beam will travel with the only real limitation being the curvature of the earth⁷.

A microwave dish can be seen at the top of the mast in one of the Creslow rebuild photos, the building that can be seen through the steelworks of the unfinished transmitter hall is still present today hence confirming that this image was taken facing north. Gawcott appeared to have a microwave link atop its transmitter hall too although from the photo its not possible to tell which way it was pointing.

Creslow’s microwave link is facing directly north (the lattice of the tower is between the rear of the dish and the camera), a line drawn in the same direction from Creslow travels straight to Hanslope Park 15 miles away which would make sense given it was the HQ at the time of the Diplomatic Wireless Service. As photos further down this blog illustrate, there is a similar radio tower attached to a building inside Hanslope Park which may well have hosted a corresponding receiver.

As for how the broadcasts came to be composed, a degree of hypothesising is required as no detail has been made public so we can only guess at what likely would have been happening.

Numbers stations are thought to be methods of sending information and instructions to agents abroad. The people needing to communicate with these people would be their agent handlers at MI6, likely based at MI6’s HQ which was Century House in London for a large part of the Cold War, 54 Broadway prior to this.

Having composed the message, this would then need to be encoded and transmitted.

Where in the system the message would be converted from clear text into numbers is unclear as is the route it would have taken to reach the transmitters. It’s conceivable that a specialist department would take responsibility for the encoding, maybe at the DWS and if Creslow’s link to the outside world was via Hanslope Park then perhaps this is where the message went from MI6’s HQ, then on to Creslow or Gawcott from there.

With need to know and compartmentalisation principles strictly adhered to, once the message was encoded then no one handling it after that point would likely know the content. It’s plausible that whilst the staff at Gawcott and Creslow would have been privy to a lot of sensitive information, the real content of what they were helping to transmit would not be amongst it, nor would who the intended recipient was or even in which country the recipient was located.

Wikipedia authoritatively indicates the site was vacated by the FCO/MI6 in 1995, it is now occupied by a web hosting company called Ecom International Network who list the site as their registered address and have been incorporated since 2012.

A more recent aerial image of the Creslow site emphasises its remote location. The markings in the fields adjacent may have been from the transmitters that once stood there⁸

There are only two planning applications viewable for the Creslow site, however despite the limited material available there are some extra clues worth noting.

The first application was lodged in April 2000 and was for a change of usage, the second was from 2005 and was a renewal of the same. There’s some interesting wording on these applications with some effort made to obscure its previous usage, although it doesn’t appear everyone got the same message about keeping things under wraps.

The original usage for the Creslow site is described on a planning application as ‘government use (sui generis)’, a Latin phrase meaning “of its own kind” which can also be translated as “we don’t want to say specifically what the site was approved for, so don’t ask questions”.

As part of the 2000 planning application, councillors visited the Creslow site in November 2000 and were given a briefing by planning officers who ‘explained the background of the site, and referred to two other such sites elsewhere in the district’ – almost certainly a reference to Gawcott and Poundon.

The attempt at maintaining a consistent cover story broke down entirely when the planning application was renewed in 2005, this time the address was given as ‘Former Early Warning Station Creslow Buckinghamshire’ and the building being described on the application for as a ‘former government/MOD listening station’.

Floor plans for the main building were included as part of the 2005 application also –

Floor plans for the main building at Creslow

Creslow Park now has its own website and even a Twitter/X account – the sort of promotion the old tenants were understandably keen to avoid.

It is also the home to a restoration project in which a group of computer enthusiasts are working to bring back to life a 1960s vintage IBM 360 Model 20. It’s been over a year since there’s last been an update on the team’s blog however there are several photos showing the inside of Creslow’s central machine hall –

Inside Creslow’s machine hall – back in the early 90s this would have been one of the most secret rooms in the country⁹

Whilst Creslow closed its gates in the 90s, another building of a very similar design and possibly purpose is still in current usage down the road within the HMGCC compound at Hanslope Park. This may be the Central Receiving Station, the role of which will be mentioned in the next post in this series about the final site – Poundon.

A similar building to that seen at Creslow within the HMGCC site at Hanslope Park¹⁰

Prior to Creslow’s closure presumably a tall aerial tower sat atop the metal caging on the building’s east side as the tower looks to do on similar construction at Hanslope.

As with Poundon, the reason for what feels to be a very sudden closure of the Creslow site so soon after a hugely costly rebuild is a mystery – the paint was barely dry before the for sale signs went up. There was a new government elected in 1997 so maybe priorities changed and Tory plans were overturned or maybe the sites were compromised in some way?