Britain would be foolish to turn its back on the “golden era” of relations with China, Beijing’s official news agency has claimed, dismissing concerns over Chinese involvement in the Hinkley Point nuclear project as “China-phobia”.

Since becoming Prime Minister last month Theresa May has stepped back from David Cameron and George Osborne’s energetic and controversial courtship of China, infuriating Beijing by postponing a final decision on the approval of the proposed £18bn ($23.5bn) nuclear power station.

In a letter to Chinese president Xi Jinping this week, May said she looked forward to “strengthening cooperation with China on trade and business and on global issues” and confirmed she would attend the G20 summit being hosted by the Chinese city of Hangzhou on 4-5 September.

A Downing Street source told the Guardian the letter was intended to reassure Beijing “of our commitment to Anglo-Chinese relations”.

However, May and her advisers are believed to have misgivings about the closeness to Beijing that developed under her Conservative party predecessor.

Writing last October, May’s influential joint chief-of-staff, Nick Timothy, questioned the wisdom of the so-called “golden” relationship negotiated by Cameron and Xi.

In an article for the Conservative Home website, Timothy claimed Beijing was using economic opportunities to buy Britain’s silence over human rights abuses and said it was “baffling” that China would be allowed to play a role in such sensitive sectors as energy and communications.

In an English-language op-ed published this week, Xinhua said the reassurances in May’s letter over Britain’s continued commitment to the “golden era” was “a laudable move in the right direction”.

However, the Communist party controlled news agency hinted that future commercial opportunities with China would depend on approval of the Hinkley Point project, a final decision on which is now scheduled for the autumn.

“After divorcing the EU, Britain would be foolish to decline stronger trade ties with China, whose markets remain home to tremendous business opportunities,” argued the article, which was penned by journalist Zhu Junqing.

“The worries over the plant are as groundless as they are unnecessary,” the article added, claiming it would be “commercially suicidal” for China to use the project to damage Britain’s national security.

“London’s misgivings over Chinese involvement in its key infrastructure is yet another stroke of China-phobia,” Xinhua claimed.

During a trip to China this week, Alok Sharma, the UK’s minister for Asia and the Pacific, said Britain’s relationship with China was “strong, growing and delivering benefits for both our countries”.

However, the word “golden” was notably absent from Sharma’s statements.

Earlier this month Liu Xiaoming, China’s ambassador to the UK, said ties between the two nations had reached a “crucial historical juncture” in the wake of the Hinkley Point postponement.