Hidden behind five rings of barbed wire in a park just outside Milton Keynes lies no ordinary manufacturing workshop. It has never opened its doors to the media in its 85-year history – until now.

At His Majesty’s Government Communications Centre (HMGCC) at Hanslope Park, what appear to be everyday objects are produced.

But that is far from the full story – with a history involving codebreaker Alan Turing, sealed rooms, and comparisons to top-secret gadgets from James Bond films.

The reason for the tight security? These objects are made for the UK’s spies and help to disguise their work.

With the BBC given exclusive access to its sprawling facility, our phones have to be handed in and security staff accompany us at all times.

We get a glimpse – but not much more – of what goes on inside as HMGCC seeks to build new partnerships to stay ahead in the spy game.

“We’ve made it really difficult for people to connect with us and that, through our history, has been a really good way of working,” explains CEO George Williamson.

But he says it is now time to change – even if that does feel “strange”.

With its anonymous-looking buildings, the place looks like an industrial estate.

Engineers, physicists, chemists, designers, coders and other specialists work on what is described rather hazily as a “mix of artistry and engineering”.

In some areas we have to wear anti-static clothing, while in others we are shown a bewildering variety of machines. They include ones that make electronic circuit boards, laser cutters and 3D printers (labelled Darth Vader, Luke and Leia in a tribute to Star Wars).

But what exactly are the machines’ creations used for? Part of the problem is that, despite my best efforts, no one will say. That is because the devices that come out the other end are highly classified.

But you can get a clue from the past. HMGCC was created on the eve of World War Two when spies and diplomats in Europe needed to communicate secretly and securely with the UK.

That led to the creation of covert radio systems which could be smuggled in a diplomatic pouch. Some of these were used by officials fleeing Warsaw as the Germans invaded Poland in 1939 to provide news of what was happening.

By the time the war got under way, this evolved into building smaller radio sets which could be given to agents from MI6 who were parachuted behind enemy lines in occupied Europe to send back intelligence.

During the war, Turing lived and worked at Hanslope Park. Most famous for breaking Nazi codes at nearby Bletchley Park, he worked at HMGCC to develop a device that could provide speech encryption.

The existing system used by wartime leaders Winston Churchill and Franklin D Roosevelt weighed 50 tonnes. Turing’s prototype, Delilah, overlaid noise from a record turntable onto speech. It was portable, ahead of its time and is another clue to what is built there today.

“I suspect you can trace a timeline directly back to what was happening there 70 or 80 years ago,” Turing’s nephew Sir Dermot Turing tells the BBC.

“The need for secure communications hasn’t gone away.”

So how does this relate to the modern world? These days, undercover agents operating in what are called “denied areas” like Russia or Iran need to communicate.

While HMGCC will not comment, other sources say modern-day spies rely on things like clandestine-burst transmitters. These can be made to look like ordinary objects and send information in fractions of a second. I’m imagining that is what is made here – but no-one wants to say.

Another object I’m shown provides a further clue to what HMGCC does.

It is a car radio speaker dating back to the 1930s. Hidden in the back is a secret transmitter.

Communication is one part of the job. But so, it seems, are concealed bugging and tracking devices although, again, officials remain extremely tight-lipped when I ask them.

“For most of our 85 years we have been producing secure communications systems that enable people in often difficult, dangerous, remote locations to communicate in secrecy back to the UK,” Mr Williamson says.

“For some of our domestic national security agencies, we may help with some of their investigative work producing technologies that help them do things like surveillance.”

One of HMGCC’s customers is MI5, who may need to secretly listen to a suspect at their house in the UK, or track them in a vehicle.

This could involve disguising a listening device as an everyday object that nobody would spot. Quite what that could be is something else no-one wants to discuss.

The temptation is to say all of this is like Q branch from James Bond. Insiders say the comparison is not quite right – I assume because they do not make things that blow up, or cars with rocket launchers, but it is hard to be totally sure.

In one room with a rubber floor, two members of staff are testing electrical devices to make sure they do not give anyone an unintended shock. Elsewhere, items made here are tested in extremes of heat and cold to make sure they can still transmit and receive.

One of the stranger places I’m shown is called Stargate, a sealed container lined with small grey foam spikes. When I am locked in, it feels a little like a modern version of a medieval torture chamber.

The room has a turntable that moves a device around, with sensors testing what kind of pattern a particular communications device emits.

That might help discover how likely it is to be spotted by a hostile state and also, perhaps, how to identify any devices they are using in your territory.

Within some pretty strict limits, HMGCC is opening up because it knows new technology that could be vital to its mission is being developed in small start-ups and in academia.

The technology could relate to fields far from national security – but there could be uses developers are unaware of.

Previously, strict security would have made collaboration impossible, but the hope is it could now happen.

“The idea is that we can take our engineers and their great ideas and put them in the same room as people from industry or academia,” Mr Williamson says.

“In that magical moment when you have different ideas coming together, something really special will emerge.”

But how that technology ends up being used is likely to remain as secret as almost everything else at this site.