And the UK has become the second most popular destination for Chinese investment in Europe, second only to Italy

And the UK has become the second most popular destination for Chinese investment in Europe, second only to Italy

Many investors worry that those economic ties will be damaged if Brexit occurs

John Zai is one of them. Originally from Shanghai, he heads Cocoon Networks, a venture capital group that plans to invest in tech companies in Europe, primarily in the UK

It’s just signed a 10-year lease on the former London Stock Exchange and aims to transform it into Europe’s largest tech innovation centre

"If we can combine the European technology and the ideas with the Chinese money, the Chinese capital, it’s going to be crazy," he enthuses

"It’s going to probably cause a lot of problems, because Cocoon is a platform bridge between China and Europe

"Tech companies are really dependent on talent," he says. "If the UK leaves the EU, all this different talent from the EU, from all these different countries, they’re going to be gone

"People are always talking about how London is going to become a Silicon Valley but without all this talent, it’s not going to happen."

Many hope the UK’s economy will flourish because of the close relationship between London and Beijing

Deals worth more than ?40bn ($56bn) were signed when Chinese President Xi Jinping visited the UK last October

During that visit, Mr Xi made his views clear: China supports a "united EU"

"China definitely wants to sell more Chinese products into the European market, but they’d better do it from the eurozone really," says Philippe Le Corre, a visiting fellow at the Brookings Institution in Washington

London would be less attractive to investors if it could offer only the UK market of 65 million people, rather than the 500 million across the EU, he says

"London would not lose its role as trader of renminbi but in terms of consumer products, big industries, even tourism, I believe London would be affected."

During his time in power, over almost four years, he’s fostered closerties with London - a counterbalance, perhaps, to China’s rockier relations elsewhere

If the UK leaves the EU, Mr Xi’s judgement could be called into question

"There has been some criticism that he has been spending too much attention on ceremonial matters and diplomacy without concern for the slowing Chinese economy at home," says Yu Jie, the China programme manager at the LSE Ideas think tank in London

"So, if the UK leaves the EU, it won’t only undermine the Chinese relationship with the UK. It will also undermine Xi Jinping’s image as a steady leader because he’s betting on the wrong horse."

Chinese entrepreneurs might also come to feel that they’ve bet on the wrong horse. Over tea at his private members’ club, Mr Zai admits to worries

"I’m just afraid if we leave the EU, it’s going to be like an earthquake, like a huge earthquake. To be honest, I have no idea what’s going to happen. Personally, I’m quite nervous."

Nerves in London stretching all the way to the halls of power in Beijing

Some might argue that Chinese concerns shouldn’t matter and British voters will make their own decisions on EU membership

But those who have invested financial and political capital in a closer relationship between China and the UK might be heading for a few sleepless nights