The Conservative Government has defended its handling of an £18bn Chinese-backed deal to build a new nuclear power plant, following criticism from Beijing.

Prime Minister Theresa May stunned the energy sector and the international community when she ordered an eleventh hour pause in the project last month.

She had been expected to rubber stamp the Hinkley Point development.

Within days former ministers accused Mrs May of harbouring suspicions about the national security implications of Chinese investment in UK infrastructure.

The Chinese government has now warned that relations between London and Beijing are at a "critical” juncture.

It signalled its discontent with a message from the Chinese ambassador to London.

He called for a quick decision on the project, in which his country has a one-third stake, and said he hoped the UK would "keep its door open" to the Asian giant.

Liu Xiaoming, writing in the Financial Times, pointed to China's record of 30 years of safe operation of nuclear facilities.

Chinese companies had invested more in the UK than in Germany, France and Italy combined in the last five years, he added, in part because of a sense of mutual trust and respect.

"Right now, the China-UK relationship is at a crucial historical juncture," he added.

"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."

He said that it had not been easy for the two countries to come this far: "As long as both sides cherish what has been achieved and continue to expand and deepen our co-operation across the board, bilateral relations will maintain their strong momentum and work for the well-being of both the Chinese and British people."

A UK Government spokesman said that Mrs May had been right to order a review of the scheme.

"As we've already made clear, this decision is about a huge infrastructure project and it's right that the new Government carefully considers it," he said.

"We co-operate with China on a broad range of areas from the global economy to international issues and we will continue to seek a strong relationship with China.

"The message that we continue to take to the world is that Britain remains open for business and we are the same outward-looking, globally minded country we have always been."

Jon Trickett, Labour's shadow business secretary, accused Mrs May of "bungling" negotiations.

He added: "I am deeply concerned whether the Prime Minister has the diplomatic skills that are needed to renegotiate Britain's trade relations with the rest of the world.

"This is the person, after all, that chose to appoint a Foreign Secretary (Boris Johnson) with the sensitivity of a clown.

"But any loss of Chinese investment matters all the more because of this Government's continued failure to develop a modern industrial strategy and provide the infrastructure and other investment needed to deliver it."