America's 160th richest person, a billionaire who made his money from the 1990s hi-tech boom, has been accused of planning to build a "secret and convenient lair" underneath his California mansion dedicated to drug-taking and sex with prostitutes.

Henry Nicholas, the CEO of the computer chip-making firm Broadcom until three years ago, has twice been accused of debauchery. The first claim was made by builders saying they were hired to build the hideaway at his home in Laguna Hills. The second claim comes from a former employee who has filed legal papers claiming $150,000 in unpaid salary.

Kenji Kato worked for Mr Nicholas as an assistant for seven years and alleges the tycoon ordered him to provide balloons filled with the laughing gas nitrous oxide for guests at parties held by the businessman. Guests' drinks would be spiked with powdered ecstasy pills, he alleges. [...]

Mr Nicholas, whose luxurious Laguna Hills home sits atop a network of tunnels and a 2,000 sq ft bar called "Nick's cafe", faces further inquiries from investigators looking at whether he handed out share options on Broadcom stock at manipulated prices.