The Duke and Duchess of Cambridge joined China's visiting president Xi Jinping as British and Chinese technology and creativity collaborations were showcased.
Ahead of talks with David Cameron at Downing Street, the Chinese leader saw objects ranging from Doctor Who's Tardis and a Dalek to a prototype zero-emission London red bus with William and Kate.
In the imposing setting of Lancaster House in central London, companies and institutions had set up stands to highlight their products and services.
The weather was typically British, with persistent rain falling when the royal couple and the foreign head of state arrived and they began their tour by seeing three famous vehicles in the courtyard of the historic house.
Before them were a black cab, London red bus and an Aston Martin sports car - all prototype zero-emission vehicles or capable of producing no emissions.
Aston Martin has unveiled a £50 million deal with China Equity to develop its zero-emission RapidE sports car.
London Taxi Company owner Geely, a Chinese business, has also announced a further £50 million investment to enhance their research capabilities and launch a new fleet of zero emission-capable black cabs.
British bus builder Alexander Dennis Limited is to join forces with Chinese firm BYD, which built the prototype bus on display, to build 200 next-generation buses over the next 10 years.
Mr Cameron will host talks with Mr Xi at Downing Street to cement multibillion-pound trade deals.
Investment by Beijing in Britain's first UK nuclear power plant in a generation is expected to be confirmed as part of what the Government hopes will amount altogether to £30 billion of agreements.
But the lavish welcome given to the president was attacked as a ''national humiliation'' by a former close adviser to the Prime Minister, who is under pressure to raise concerns about human rights and "dumped" cheap steel blamed for the loss of thousands of British jobs.
Ex-Number 10 policy guru Steve Hilton said the UK should be imposing sanctions, not rolling out the red carpet.
Downing Street has fiercely resisted claims the UK is "kowtowing" to the Chinese and insisted no subjects were off the table for the leaders' meetings - which will also include lunch at the PM's rural retreat Chequers tomorrow.