The Chinese government unveiled a guideline in September that allows "non-state" capital to invest in some state-owned companies to form "mixed ownerships", considered by many private investors to be a huge opportunity - if it goes well.

China has more than 155,000 SOEs, ranging from some of the world's biggest banks and oil companies to smaller local firms, holding more than 104 trillion yuan (HK$127 trillion) in assets as of 2013, according to official figures.

Although foreign investors are still barred from certain industries and subject to national security reviews, some British companies are already looking at opportunities to either acquire non-core assets from the SOEs or to form partnerships to help develop their property assets, areas in which the UK firms have great expertise.

"Our businesses will be very interested to hear more about how the SOE reforms will progress," Sassoon said.

Shortening the so-called negative list of excluded industries for the Shanghai Free-Trade Zone (FTZ) is also strongly desired by the British side, and a specific financial services group discussion will take place during state visit, he added.

In a well-received move, the Shanghai FTZ gave the green light for the entry of foreign insurance brokers.

But the list of exemptions was still too long for British firms, who are eager to promote their world-leading financial and business services to the limited Chinese market.

Xi's visit includes tours showcasing British creativity, design and science - sectors looking at more access to the China market.

Intellectual property issues would be a focus of discussions during the visit, Sassoon said.

"These are so important to British design and technology companies," he said.

People needed to remain realistic about what would come out of Xi's visit, Sassoon added. A state visit, with so many political and ceremonial arrangements, had a different dynamic to a regular visit. But warm, friendly and positive relationships between the two countries would certainly help tackle problems in business.

"The bottom line of what British businesses want to see is consistency in policymaking, to continue to carry forward the very important initiatives under the 'New Normal' financial conditions regarding free-trade zones, to reduce the number of items on the negative list, and see details of SOE reform," he said.

Despite China's slowing economic growth, opportunities in the world's second largest economy were still huge. "If China were to continue to grow at 7 per cent, it would generate the equivalent of the UK economy in four years," Sassoon said.

Xi's visit will be highlighted by some massive infrastructure deals, including China's £25 billion (HK$300 billion) investment in the Hinkley Point nuclear power plant, possibly followed by more proposed nuclear plants, and possible cooperation in Britain's £12 billion high-speed rail line.

Involving Chinese investment in fundamental infrastructure projects was an indication of Britain's openness, said ambassador to China, Barbara Woodward.

Sassoon said tt was also a strategic positioning of Sino-British economic cooperation, in particular as Britain faced competition from is European rivals.

Germany's strong relationship with China is based manufacturing; for France it is nuclear technology. Sassoon's first meeting as commercial secretary in 2010 was with China's ambassador to Britain, Liu Xiaoming , on a possible central plank of the Sino-British commercial and economic relationship. Eventually, infrastructure was identified.

On the eve of Xi's visit, the "golden era" - to use British Prime Minister David Cameron's words - between the two economies seems to have begun.

"The UK started behind some of other European countries, but we've been catching up and overtaking our rivals," Sassoon said.