The council found he had an undeclared bank account into which large cash deposits were made, it said.
In February 2016, £18,000 was placed in it. In April 2016, there were two deposits: one of £126,000 and another for £19,000.
The largest arrived in April 2018 when £185,000 appeared.
Investigators discovered more than £397,000 was spent between February 2016 and July 2019 at places including Mayfair restaurants, Harrods and The Ritz.
He enjoyed private jet travel and paid school fees, the council said.
In October 2020, the council said, he was arrested and documents discussing shareholdings and pensions were seized.
Photos showing a high-value lifestyle were found.
The council’s revenues, benefits and fraud chief, Simon Rosser, dubbed the fraud “complex”.
“Our fraud team works closely with internal services and external partners to ensure public funds are protected and that those who deliberately seek to abuse the system are identified and held to account,” he said.