Its state-of-the-art surveillance cameras monitor the movements of millions of Britons going about their daily lives in airports, government buildings, sports stadiums, high streets and stations.

Hikvision, a company controlled by the Chinese government, was recently revealed to be Britain's biggest supplier of CCTV equipment, raising fears its internet-linked cameras could be hacked from Beijing at the touch of a button.

Last week, undercover Mail on Sunday reporters posed as businessmen to infiltrate its headquarters in the 'surveillance city' of Hangzhou in eastern China, to investigate its activities.

What they found will raise fresh cause for concern about a company whose growing influence in the UK has already been questioned by former MI6 officers and Security Ministers. Far from being the independently run business it claims to be in its customer-friendly marketing, Hikvision is controlled by China's ruling Communist Party.

Hi-tech surveillance, face recognition software and equipment is used inside the headquarters of Hikvision in Hangzhou, China

Hikvision is central to the government's Orwellian programme to spy on its 1.3 billion citizens, and is inextricably linked to the totalitarian crackdown on those considered 'enemies of the state'.

More worryingly, Hikvision vice-president Pu Shiliang, 38, is also technical leader of a key laboratory at the Ministry of Public Security, the feared body that has been accused of the extrajudicial arrest and detention of thousands of lawyers, activists and perceived government opponents within China every year.

Hikvision's high-tech CCTV systems can 'see in the dark', track vehicles, and count the number of people entering and leaving a building, as well as boasting unparalleled 'face-tracking' technology.

They are even able identify a person by their gait.

These capacities enable the Chinese authorities to track dissidents, activists and human-rights campaigners, who are routinely rounded up and detained.

Last night, Lord West of Spithead, a Security Minister under Labour, said: 'We know very well that the Chinese hack Western systems on a massive scale to get intellectual property, but this is even more worrying. If these cameras were in an office, they could see all the paperwork and get names of employees.

'What I've been pushing for is for the Government to set up a group that looks at the implications of all these decisions, and that should include the security agencies.

'The Chinese are hacking on a massive scale and if people do that, it's only right that we look at the implications.

'Yes, we want to trade with them, but people have to play by certain rules.'

Hikvision has been bankrolled to the tune of billions of pounds from Beijing, using the funding to sell CCTV systems at what critics claim are below market prices, and enabling it to become the world's biggest video surveillance system company in under a decade.

But until now, no one has seen behind the darkened glass windows of its headquarters in Hangzhou.

The Mail on Sunday was shown surveillance systems capable of singling out 'targets' in crowds within seconds by studying their faces and gait. Officials candidly told us their cameras in cities across China are controlled by the government which used them to track wanted people on a vast database of 'bad guys'.

Hikvision is central to the government's Orwellian programme to spy on its 1.3 billion citizens

They also told us government officials used the G20 summit in Hangzhou last month, attended by Barack Obama, Angela Merkel and Theresa May, to test the system's latest people-watching capabilities.

The China-wide project using products made by Hikvision and other smaller technology companies is called Skynet – the same name as the malignant Artificial Intelligence system bent on destroying humanity in the Terminator films.

And while Hikvision tells customers Skynet is an anti-crime initiative, government policy documents declare that its primary aim is to prevent public protests and 'find and control hostile forces' threatening China's repressive one-party state.

The revelations raise uncomfortable questions over whether Hikvision – now the biggest security camera provider in Britain with 20 per cent of the market – should be allowed unfettered access to the UK, and why it has never been subjected to security checks.

Experts fear Hikvision's internet-linked surveillance systems could potentially be remotely hacked from China through so-called 'back door' loopholes and used to track dissidents and human rights campaigners seeking refuge in the UK.

Nigel Inkster, a former deputy chief of MI6, said: 'There's probably a good case for a government look at this – who controls or has access to significant amounts of our national infrastructure.'

We have many customers in Britain now. It is one of our biggest overseas markets after the US. Hikvision official

The firm's systems are in use on the London Underground network and in city centre surveillance in Salford, Manchester, and Hammersmith and Fulham in London, including at Chelsea Football Club.

Managers at Hikvision agreed to give us a tour of the research and development facilities, apparently keen to drum up more orders from overseas clients. In a suite of showrooms, we were shown surveillance cameras capable of seeing through fog and dark, and systems that can read vehicle number plates. The systems' advanced technology can also give accurate estimates of a target's age, sex and height.

'We have many customers in Britain now,' a company official told us. 'It is one of our biggest overseas markets after the US.'

Hikvision, which has 17,000 employees, says its urban surveillance systems target criminals and terrorists. 'We call it our safe city project,' the official said. 'Our cameras help to make a better world, a better city. If someone has committed a crime and walks across this camera area they will be identified from the database and the information will be instantly sent to the police.'

In an attempt to address privacy concerns, the official added: 'We just provide the cameras. We do not use the database ourselves, so people's privacy is protected. It is the government that controls the cameras and the database.'

China's leader Xi Jinping – who has led a ruthless crackdown on dissidents since his appointment in 2013 – visited Hikvision's HQ last year, praising its work and applauding the company for having a workforce with an average age of just 28.

Despite claiming on its website to be 'an independent and publicly traded corporation', Hikvision is in fact owned by the Chinese Electronic Technology Corporation, a government body tasked with developing electronic systems for military and civilian use, including developing software to collate data on the jobs, hobbies, consumption habits and other behaviour of citizens to identify 'terrorists'.

Hikvision, a company controlled by the Chinese government, was recently revealed to be Britain's biggest supplier of CCTV equipment

As it rapidly expands its global presence, Hikvision has been generously bankrolled by Chinese state banks, which critics say give it an unfair commercial edge.

It received £2.4 billion from China Development Bank in December and a further £2.3 billion loan from the Export-Import Bank of China in August, both of which are controlled by the Chinese government.

Weeks before our visit, Hangzhou hosted the G20 summit and tens of thousands of additional Hikvision surveillance cameras were put in place on key road junctions and buildings. Every taxi and bus also had miniature security cameras installed. Today, there are an estimated 600,000 CCTV cameras in Hangzhou – one for every ten residents – making it one of the world's most watched cities along with the capital Beijing, which state media boasts is now '100 per cent covered' by surveillance cameras.

'You can be watched anywhere you go in Hangzhou,' the company official told us, adding that the G20 was used to test the efficiency of the latest Skynet systems. 'It was like an experiment,' he said.

The Chinese government's bid to expand Skynet reflects its paranoid determination to wipe out any opposition to the Communist Party as its economy stutters. A government document on Skynet issued in 2005 stated that its main aim was not to prevent normal crime but to maintain 'social stability… find out and control hostile forces' and to 'prevent mass disturbances in public areas'.

In the north-eastern city of Changchun, there was an outcry in 2013 when hundreds of thousands of surveillance cameras failed to find any trace of a car stolen from outside a supermarket with a sleeping two-year-old baby boy in the back. The boy was later found murdered.

'Skynet is useless. It isn't for public protection – it is just for following dissidents,' one furious resident said on an online forum.

Last night, Sir Malcolm Rifkind, former chairman of Parliament's Intelligence and Security Committee, said: 'There's clearly going to be a series of these Chinese-related projects and some may or may not have national security implications. There's going to be a need for a more joined-up strategy. You can't automatically say all business with China is dangerous but the security agencies can give expert judgment on the technical possibilities of another government accessing systems.'

John Honovich, head of the surveillance industry monitor IPVM, said the systems developed by Hikvision gave the Chinese government 'a powerful means to monitor and suppress any opposition to the party'. He said Hikvision was being heavily funded by China's state banks in a push to give it global dominance, allowing it to undercut rivals and sell systems overseas at relatively low prices.

'The overall strategic goal is to maximise market share, even at the expense of losses,' he added.