Government struggles to corroborate PM’s disputed figure as some of the deals listed have eerie similarity to ones made in past

Downing Street has insisted that the week-long Chinese state visit secured “up to £40bn” of trade and investment deals, after scrambling for much of Friday to substantiate the figure, brandished by David Cameron at a trade mission in Mansion House.

The business secretary, Sajid Javid, said earlier this week that President Xi Jinping’s visit would increase trade and investment between Britain and China by £25bn; but the figure had leapt to £40bn by the time the prime minister spoke on Wednesday.

No 10 officials remained coy throughout much of Friday about precisely how that figure had been arrived at, claiming repeatedly that full details would be published when the state visit had officially ended.

A statement was finally released after 6pm, detailing a long list of deals, including a promise from Chinese firm HNA to buy £1.4bn-worth of Rolls-Royce jet engines, to be built in Derby; and £6bn worth of investment in the Hinkley Point nuclear power plant.

But some of the agreements had a familiar ring about them. A £1bn memorandum of understanding about a “garden of ideas” – a pleasure garden to be built in China, in association with the Eden Project – appeared strikingly similar to a deal signed, in the presence of George Osborne, in 2014.

Doubts were also raised about £6bn of investment “to help fund regenerative medicine and tissue engineering research with Oxford University” – apparently the same deal announced by the university earlier this week as worth just £1.5m. No 10 said this was based on the Chinese bank behind the investment pencilling in a total of £6bn.

The decision by Chinese firm Sanpower, which owns House of Fraser, to open the department store’s first branches in China was first reported in April – and ultimately involves a Chinese investor, expanding in its own domestic market, albeit behind a British shopfront.

Other items referred to Chinese cash “unlocking” investment, before apparently listing the total value of the project in question, for example: “Hualing’s investment will unlock three major regeneration projects in Leeds, Manchester and Sheffield with a combined gross development value of £1.2bn.”

The government also trumpteted an announcement by BP that it would sell China’s Huadian Corporation up to 1m tonnes of liquid natural gas each year, valued at £6.5bn; but the income from it will be spread over two decades.

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The previous public statement from UKTI, the government’s trade and investment arm, referred to deals worth “£BILLIONS”, and press officers spent the day referring all enquiries to Downing Street.

Osborne has been keen to secure fresh Chinese investment, including in his “northern powerhouse” project. On a recent trip to the city of Chengdu, he opened up what he called a “northern pitchbook”, encouraging firms to bid on everything from construction of the HS2 high-speed rail link, to a new science park in Newcastle.

But the welcome accorded to the Chinese delegation was particularly controversial, taking place against the backdrop of thousands of job cuts in a steel industry which blames Chinese cut-price competition for its demise.

Other deals that had been highlighted during the trip, including a commitment by BBC Worldwide to make a number of programmes including a Chinese version of the long-running series Coast, were not listed by the government because of, “commercial sensitivities or confidentiality”.

Speaking at the UK-China business summit earlier in the week at which many of the deals were signed, Javid said: “A forum like this where business leaders from both countries can come together and make deals for our mutual benefit is greatly rewarding for the prosperity of all our people.”