It could be the home of a real-life Wernham Hogg, the fictional firm in Ricky Gervais's hit comedy The Office.
The nondescript unit is in an 'office village' on the outskirts of the Oxfordshire town of Banbury, close to the M40 motorway and in the shadow of an enormous Amazon warehouse shipping goods around the UK.
But in fact this is the home of a secret operation nicknamed 'The Cell', tasked with making sure that Chinese tech giant Huawei isn't helping the Communist state to spy on Britain.
And it's totally tip-top secret - right up to the massive sign on the front that announces the presence of the Huawei Cyber Security Evaluation Centre (HCSEC).
It is immediately visible to anyone wandering past - admittedly probably not that many - but also to millions via Google Street View.
Part of the National Cyber Security Centre (NCSC), this is where spooks decided that Huawei could be allowed to take part in the UK's 5G network, a decision that has angered Washington and Tory back-benchers alike.
The set of rooms in Endeavour House is owned by Huawei and is the home base of around 35 staff from the HCSEC, which was set up in 2010.
At this out-of-the-way site they test equipment supplied by Huawei, destined for use in the UK.
Crucially, the Cell has the only access to Huawei’s confidential ‘source code’ and is the only facility that can really test whether there are vulnerabilities that could allow ‘back-door’ access to networks.
Since 2014 the work of the British nationals employed there has been monitored by GCHQ, the Cabinet Office and Home Office.
While Huawei is a private firm, critics say it is part of China's state security apparatus and could be used as a cover for espionage, which is why yesterday's 5G decision is so controversial.
It's totally tip-top secret - right up to the massive sign on the front that announces the presence of the Huawei Cyber Security Evaluation Centre (HCSEC)
Covert: Endeavour House, on the outskirts of Banbury, has tinted windows that protect the highly confidential work going on inside
Boris Johnson was accused today of defying misgivings from his own ministers to press ahead with letting Huawei have a role in the 5G network.
Huawei has come under scrutiny over allegations of close ties to the Chinese state.
Founder Ren Zhengfei's past links to the military have been cited as a concern, as has China's history of state sponsorship and surveillance.
Chinese law can also compel firms to co-operate with Chinese national intelligence work, which some critics have suggested could see Beijing require Huawei to spy on people through so-called 'back doors' in its telecoms equipment.
Huawei has vehemently denied the allegations of any ties with the Chinese state and says it abides by the laws of every country in which it operates.
Defence Secretary Ben Wallace is said to have urged the PM at a crunch National Security Council meeting to heed warnings from the US over the Chinese tech giant.
Mr Wallace branded Beijing a 'friend of no-one', according to the Times - but eventually accepted the decision to allow the firm 'limited' involvement in the infrastructure project.
The wrangling emerged as US Secretary of State Mike Pompeo flies into Britain for what could be a turbulent visit.
The White House voiced 'disappointment' over the decision, after intensely lobbying for the UK to shun Huawei.
According to its 2019 report, the HCSEC's oversight board is made up of a mixture of security service figures and senior Huawei managers.
The board is chaired by Ciaran Martin, the NCSC's chief executive, with Huaswei's executive director Ryan Ding as his deputy.
The Government acknowledged Huawei is a 'high risk vendor' but argues that it will not have a role in the core parts of the 5G network
And the same document, released last March said its work 'has continued to identify concerning issues in Huawei’s approach to software development bringing significantly increased risk to UK operators, which requires ongoing management and mitigation'.
As the Government gave the green light for the controversial Chinese tech firm to play a limited role in the UK's 5G network, the NCSC said the risk of its involvement was 'manageable'.
Huawei is already subject to oversight arrangements which ensure that any 'embedded malicious functionality could be detected should it exist', the analysis said.
The NCSC said: 'Due to the UK's mitigation strategy, which includes HCSEC as an essential component, our assessment is that the risk of trojan functionality in Huawei equipment remains manageable.
Huawei has invested billions of pounds into research and development around 5G network infrastructure and, as a result, is now considered the industry leader in 5G technology.
It is also already part of the existing network infrastructure in a number of countries, including in the UK.
As a result, using one of Huawei's rivals, and most likely alternatives - Ericsson or Nokia - for the building of 5G networks, would likely cause a delay and add cost to the introduction of widespread 5G in the UK.
In contrast, none of the four largest mobile carriers in the United States use Huawei equipment in their networks.
'Placing ''backdoors'' in any Huawei equipment supplied into the UK is not the lowest risk, easiest to perform or most effective means for the Chinese state to perform a major cyber attack on UK telecoms networks today.'
The NCSC did raise concerns about any single supplier of equipment being allowed to play a dominant role in the network.
The guidance issued by NCSC excludes 'high-risk vendors' such as Huawei from 'core' parts of the network, and sensitive locations including nuclear sites and military bases.
They will also be limited to a minority presence of no more than 35% in the periphery of the network, known as the access network, elements which connect devices and equipment to mobile phone masts.
The NCSC stressed that it was 'important to avoid the situation in which the UK becomes nationally dependent on a particular supplier'.
It added: 'Without government intervention, the NCSC considers there to be a realistic likelihood that due to commercial factors, the UK would become ''nationally dependent'' on Huawei within three years.'
Ricky Gervais and Stephen Merchant's hit comedy The Officer was set in the nondescript, soul-destroying offices of paper manufacturer Wernham Hogg
National dependence on a high-risk vendor would present a 'significant national security risk', the NCSC said.
The advice being issued to UK telecoms operators is that 'high-risk vendors' should be:Excluded from all safety related and safety critical networks in critical national infrastructure Excluded from security critical 'core' functions, the sensitive part of the network Excluded from sensitive geographic locations, such as nuclear sites and military bases Limited to a minority presence of no more than 35 per cent in the periphery of the network, known as the access network, which connect devices and equipment to mobile phone masts
NCSC technical director Dr Ian Levy said Huawei had always been treated as a high-risk vendor and the authorities have 'worked to limit their use in the UK'.
'We've never 'trusted' Huawei and the artefacts you can see (like the Huawei Cyber Security Evaluation Centre (HCSEC) and the oversight board reports) exist because we