"Hong Kong and their classification as a developed market may be questioned at some time, if the regulation is controlled from Beijing rather than Hong Kong. I think index providers should keep a watchful eye on that," Mark Makepeace, who retired from FTSE Russell last year, told Reuters in an interview.

His comments highlight growing concern in the West over the degree of Hong Kong's autonomy from mainland China, promised under a "one country, two systems" formula when Britain handed the territory back to China in 1997. That unique system has underpinned Hong Kong's status as a developed market for decades, while mainland China was only deemed an emerging market in 2017.

Worries over Beijing's growing encroachment in Hong Kong were heightened when on Wednesday the territory's pro-democracy opposition lawmakers resigned in protest against the dismissal of four of their colleagues from the city assembly, after Beijing gave local authorities new powers to further curb dissent.

Makepeace, who is now an independent director of the Singapore Exchange board, said Hong Kong regulators have so far been "fiercely independent," but that could change.

Makepeace was speaking to Reuters ahead of Thursday's launch of his memoir on how he built FTSE into one of the world's largest indexing and financial data companies.

The book also lifts the lid on the indexing industry, which has revolutionised global investing and amassed enormous power to allocate trillions of investment dollars globally, leading some policy experts to call for tougher regulation.

Makepeace discusses his dealings with corporate giants including Glencore and Saudi Aramco, and leaders of countries all keen to be included in global benchmarks, and the political pressures sometimes brought to bear on the process.

He describes the dilemma he faced in 2018 when Saudi Arabia's Crown Prince Mohammed bin Salman was implicated in the killing of Jamal Khashoggi, a U.S.-based journalist and critic of the Saudi regime, just months after FTSE Russell announced it was promoting Saudi to emerging market status.

While Makepeace said he tried to keep politics out of such decisions, he wrestled with whether to proceed with the upgrade.

"On the one hand, there was a real political desire to do something, on the other hand what precedent does this set and where do you draw the line? In the end, we took the decision that we would continue, but it was an uncomfortable time."

(Reporting by Michelle Price; Editing by Stephen Coates)

By Michelle Price and Sumeet Chatterjee