The British financial trader accused of helping to trigger the 2010 Wall Street "Flash Crash" has lost a High Court bid for bail after a judge ruled that he continues to pose "a clear flight risk".

Navinder Singh Sarao, 36, was seeking release from Wandsworth prison in south-west London while he fights extradition to America.

The extradition battle is expected to take many months.

After a judge rejected Sarao's application, his lawyers said the family was "obviously disappointed" but the door had been left "slightly ajar" for a further bail plea at a later date.

Sarao was arrested on April 21 at the request of the US authorities, who want him extradited to face allegations that he helped cause the multibillion-dollar US stock market crash from his parents' home 3,500 miles away in Hounslow, west London.

The US Justice Department claims Sarao and his company, Nav Sarao Futures Limited, made £26 million illegally over five years.

He faces 22 charges including wire fraud, commodities fraud and market manipulation, which carry sentences totalling a maximum of 380 years.

Lawyers for the former bank worker and Brunel University student argued that a bail condition imposed at Westminster Magistrates' Court that he personally pay a £5 million security was impossible to comply with - and therefore unlawful - because US authorities had obtained a worldwide freezing order on his assets.

James Lewis QC, appearing for Sarao, said his parents had offered £50,000 as a surety and were also willing to put up the value of their house as bail if the court was willing to accept it.

Mr Lewis said Sarao was from "a very tight-knit and close family" and had lived in the same house with his parents all his life and would not risk their life savings by absconding.

But Mark Summers QC, for the US government, opposed bail and said the parents' bail money and the value of their house was a "derisible" amount and "small change" compared with "the 40 million dollars of criminal profit" Sarao allegedly had at his disposal.

Mr Lewis accused the US government of "hyperbole and prejudice" and said it had taken a "disgraceful" position in a case in which Sarao claimed he was being used as a scapegoat for the market crash.

But the judge refused bail, saying: "There is a clear flight risk."

He said that was why two district judges had already refused bail without the £5 million security.

The £50,000 - compared with the alleged 40 million dollar profits Sarao had made - was "no assurance at all".

The judge said: "I accept Mr Summers' submission that until the applicant demonstrates that he has no access to any funds anywhere, so as to provide reassurance that any court in the world would want, the application is premature."

Sarao's solicitor, Richard Egan, said after the ruling the family was "obviously disappointed", but added: "The door has been left slightly ajar for us to come back again."