China's ambassador to Britain urged London on Tuesday to approve a Beijing-funded nuclear power plant as soon as possible, warning that relations between the two countries were at a critical point.

"Right now, the China-UK relationship is at a crucial historical juncture. Mutual trust should be treasured even more," Liu Xiaoming wrote in an article in the Financial Times newspaper.

"I hope the UK will keep its door open to China and that the British government will continue to support Hinkley Point -- and come to a decision as soon as possible so that the project can proceed smoothly."

On July 28, Britain's new government said it was delaying final approval of the 18-billion pound (21-billion-euro, $23 billion) project to build Hinkley Point, the country's first new nuclear plant in a generation.

China General Nuclear Power Corporation (CGN) is due to take a 6-billion pound stake in the project, which will be led by French energy giant EDF.

Analysts warned the delay could jeopardise ties between Britain and China, the world's second biggest economy, at a time when London needs to build strong trade ties following its june vote to leave the European Union.

Chinese official Xinhua news agency had reacted to the delay by saying it "adds uncertainties to the 'Golden Era' of China-UK ties" -- but the ambassador's comments went further.

The delay on a final decision, which is now expected in September, appeared to mark a change in attitude by Britain's new Prime Minister Theresa May.

Her predecessor David Cameron, who stepped down after the Brexit vote, had made ties with Beijing central to his economic policy.

There are questions in Britain over whether Hinkley Point represents value for money and regarding its environmental credentials.

One of May's top aides has also previously raised the issue of a potential threat to Britain's national security.

The project is also controversial in France, dividing the top management of EDF and sparking strong opposition from trade unions, which fear it might bankrupt the utility, in which the state has a 85-percent stake.

French President Francois Hollande backs EDF's involvement, but a statement issued by his Socialist party late Monday suggested a cooling of support.

Noting the importance of the project for EDF's future prospects, it said "all questions and reservations should be resolved before going further".