London | Lex Greensill, born and bred on Australia’s largest sweet potato farm, is a man of the soil. But as he cultivated a $6 billion financial empire this past decade, he’s ventured far from his Bundaberg roots: Wall Street, the City of London, a desk at Downing Street, concerts at Buckingham Palace, an office at Davos, and almost permanent residence in his globe-trotting private jet.

Now, still only 44 years old, the high-flyer looks in danger of falling back to earth.