The building is home to Futex, one of several so-called "trading farms" in the UK that give training, office space and equipment to people prepared to make short-term trades, mostly within a day, with their own money in the hope of being hired or sponsored for a cut of their profits.

Navinder Singh Sarao - who has been accused by U.S. authorities of contributing to the May 2010 "flash crash" in Wall Street - worked there between early 2003 and early 2008, according to a statement by Futex on Friday.

"(Sarao) sat in a separate part of the company, away from the rowdy bunch," said Simon Maelzer, who worked at Futex for a few months in 2008. "He created his own space on the trading floor. I always noticed this guy, who was completely 'in the zone'."

Sarao has been charged by U.S. authorities in a criminal and civil case with fraud and market manipulation; he is currently in jail in the UK. Authorities in the United States have sought to link him to the May 6, 2010 'flash crash,' where the U.S. stock market temporarily lost $1 trillion in market value in a matter of minutes.

Maelzer, now a global macro strategist for research firm MacroVigilance.com, said that while Futex was a good company, those who joined were in for a hard ride at the start.

"The Futex set-up was tough for beginners and many would get despondent and give up, although this is typical of the futures market in general. I didn't even get a salary at all," he said.

The Futex traders - mainly men aged 25 to 35 - would make the daily commuter grind from London to Woking, around 23 miles (37 km) to the southwest, bringing their own laptops and software program, and then take on the markets in the spartan Futex office, said Maelzer.

Futex would provide them with office space, desks, terminals carrying market data and phonelines and would take on the most successful ones, such as Sarao, help to fund them and share in their profits.

For Jonathan Roy - whose first interview was at Futex after leaving Liverpool University - the fact that he had to go to Woking, an archetypal commuter town far from the glamour of the capital, was slightly offputting.

"It's a bit of a trek just to get down there."

HIGH FEES

One Futex trader described Sarao in a March YouTube clip this year as a 'legend', and an online petition was underway by other traders to block Sarao's extradition to the United States.

"He's a legend in our firm, I'd say. During the financial crisis, this guy had, for want of a better word, balls. He just used to get into big positions. He saw the risk, he saw the reward and he took on the trades," Futex trader Miltos Savvidis said in the YouTube clip.

The few, casually dressed traders outside the Futex office in Woking this week said they had been told not to comment on the situation concerning Sarao, who is opposing extradition to the United States.

Savvidis did not respond to requests sent via Futex for further comment. In a statement, the firm said it had no concerns about his trading during his tenure, which ran from early 2003 to early 2008.

"Navinder's method involved no use of algorithmic trading and as such was purely a 'point and click' style of trading whilst he was at Futex," the firm said. "His trading did not give Futex (nor the regulators) any cause for concern."

Roy decided against Futex and went to trade his own money – known as 'prop trading' – at Schneider Trading Associates in London instead.

Roy said that while he gained invaluable financial markets experience at Schneider Trading, it was very difficult to make money to start off with due to high fees for the use of the desk and commission fees on executing trades. Roy is now a partner at London-based firm Charles Hanover Investments.

"It's quite brutal to start with. We had 30 people to start with, but it was soon whittled down to about nine."

Those in the industry said that one of the challenging aspects about Futex, Schneider Trading Associates and peers such as Amplify Trading were the fees for training courses and use of the office.

Richard Edwards, who worked at various top investment banks including Lehman Brothers before setting up his own research firm HED Capital, said 9 out of 10 prop traders would lose money, but they all persisted in the hope of being the one who made it big.

"It's a heroic activity because you're betting so much, which helps the market thanks to the extra liquidity. Most of them will lose out but those who make it stand to make millions."

(Editing by Lionel Laurent, Philippa Fletcher and Nick Zieminski)

By Sudip Kar-Gupta