Wall Street "flash crash" trader Navinder Singh Sarao, wanted by US authorities over allegations he helped to wipe hundreds of billions of dollars off the value of Wall Street stocks, may have a hidden £40m offshore nest egg, according to a report.

His company's accounts show that from 2009 onwards Nav Sarao Futures Trading paid out £23.5m to an employee trust, and that a further £15m "guarantee fee" is likely to have gone to the trust, said a report in The Times.

The report came as London's Evening Standard revealed that Sarao had made more than £30m profit in trading from his parents' home in four years.

The Standard report said that after graduating from Brunel University, Sarao worked in the City before joining Woking-based Futex as a graduate trainee.A former colleague told the London paper that Sarao would arrive at the Woking office at 10am "to avoid paying peak train fares and always wore a tracksuit. He would sit with a hoodie pulled up around his head and eat discounted supermarket sandwiches late in the afternoon."

Adam Whiting, who worked next to Sarao at Futex for six months, tweeted: "One thing I will say is Nav used to wear a tracksuit every day, even when an early millionaire. From what I remember Nav only loved making money, not spending it."

Another trader, who wished to remain anonymous, described Sarao as "slightly aloof", rarely joining in the "camaraderie of the trading floor".

But neighbours spoke of their surprise at reports that Sarao ran a multi-million-pound trading operation from the three bedroom semi in Hounslow, West London. "They are not showing off with a Mercedes or something like that," Harmesh Singh Johal, a friend, told the Standard, as he gestured towards the Saraos' battered Vauxhall Corsa.

A childhood friend of Sarao, Anil Puri, also from Hounslow, added: "He was quite sweet — a chirpy chap. He was the youngest out of the lot, and he was the loudest of the lot."

Meanwhile, the US authorities have emails sent by Sarao in which he described himself to a colleague as an insomniac and explained his trading to the City watchdog as "very short term and for very small profits".

In one email, Sarao, 36, revealed that on a good day: "I normally make circa $135,000. On quieter days I look to make between $45,000 and $70,000."

Documents filed by the US Department of Justice claim that from April 2010 onwards Sarao "took significant steps to protect his assets" and pursued a "tax avoidance strategy", first setting up a company, Nav Sarao Milking Markets Ltd, in the Caribbean haven of Nevis.