LONDON (Reuters) - High-profile British Treasury Minister Jim O'Neill, a former Goldman Sachs chief economist, could quit his post over Prime Minister Theresa May's new approach to Chinese investment, the Financial Times reported, citing a friend of O'Neill.

May intervened personally last week to delay the final decision on a partly-Chinese funded nuclear power project, a source said on Saturday, while a former colleague said May had previously expressed concern about the national security implications of the planned Chinese investment.

O'Neill is a member of the unelected upper house of parliament and works in the finance ministry as Commercial Secretary, with responsibilities including infrastructure policy and promoting Britain as a source of foreign direct investment.

Widely respected and influential in the global investment community, his appointment in 2015 was considered a major coup for the British government. He kept his role despite sweeping changes to the government in July following May's promotion to leader after David Cameron's resigned.

"He’s considering why he has been asked to stay," said one friend according to the Financial Times.

The friend said O'Neill was baffled about the government’s change of tack on China, and will quit unless May can explain why she wants him to stay, according to the FT report.

The Treasury declined to comment on the report.

In her previous role as interior minister, May had expressed concerns about the government's approach to Chinese investment, citing national security concerns, according to Britain's former business secretary Vince Cable.

O'Neill had been heavily involved in former finance minister George Osborne's push for a "Golden Era" of relations between the two countries, largely based on courting Chinese investment in British infrastructure.

Osborne left the government earlier this month along with Cameron in the wake of the country's vote to leave the European Union. He was replaced by former foreign minister Philip Hammond.

China General Nuclear Power Corp (CGN) was set to invest around 6 billion pounds ($7.93 billion) for a 33 percent stake in the Hinkley Point nuclear project, paving the way for it to lead another project in Britain that would use Chinese nuclear technology.

A decision is now due by the autumn, possibly as early as September.

($1 = 0.7562 pounds)

(Reporting by William James; Editing by Marguerita Choy)