Sunak was made Britain's third prime minister in as many months in October last year as the tax-cutting fiscal plans of predecessor Liz Truss spooked markets, pushed up borrowing costs and sent investors fleeing.
In his first few months, Sunak - himself a former hedge fund manager - and his government have reversed Truss' fiscal plans, restoring some of Britain's credibility and calming markets.
But Britain faces other crises, from widespread strikes, high inflation, slow growth and a health system under strain.
Downing Street has said Sunak will not go to Davos, a Swiss resort which hosts the World Economic Forum (WEF) of business and government leaders, as he focuses on domestic challenges, but on Thursday morning he hosted a veteran of the event.
A co-founder of the world's biggest private equity firm, Schwarzman has been one of Wall Street's biggest donors to Donald Trump's election campaigns, although he has said he will not back the former U.S. president in 2024.
Schwarzman is a regular attendee of Davos and is expected to go again this year, as it returns to its winter slot following the COVID-19 pandemic.
The forum has been criticised by some as a talking shop for the jet set that merely adds to the world's carbon footprint, but the forum insists it has the power to bring decision-makers together in a world facing multiple crises.
The meeting between Sunak and Schwarzman had not been publicised. Asked about Sunak on Thursday before he left London for a trip to Scotland, his spokesperson told reporters he had "meetings all day" but declined to say who with.
Asked by Reuters later what the prime minister discussed with Schwarzman, a Downing Street spokesperson said it did not comment on meetings the prime minister may or may not have had.
Blackstone were not immediately available for comment.
(Reporting by Alistair Smout in London, additional reporting by Greg Roumeliotis in New York, editing by David Evans)
By Alistair Smout
