The practice of spoofing, where a financial trader signals orders to sell shares that they do not intend to fulfil, is not a crime in the UK and should not be used to justify the extradition of a British citizen to the US, Navinder Singh Sarao’s lawyer has told a court.

The US government alleges that Sarao’s behaviour helped cause a sharp fall in Wall Street equity prices on 6 May 2010, widely known as the “flash crash”, and is seeking his extradition to stand trial in a US court.

James Lewis QC, speaking on the second day of Sarao’s extradition hearing in London on Friday, said that in any case, the defendant was not guilty of making a false representation of his trading intentions in order to mislead the market.

He said Sarao’s frequent sell orders were genuine in the sense that, while they were in the market, they could be fulfilled and in fact sometimes were fulfilled.

“The prosecution says the defendant is guilty of spoofing and maintains that the way he traded … involved the practice of spoofing, which involves the deliberate manipulation of prices,” Lewis said.

“Without an admission as to Sarao’s conduct, I would point out that spoofing is not a crime in the UK. There has been no English case of spoofing and no one has ever been convicted in the UK.”

Sarao’s defence team is arguing that the alleged offences do not amount to an “extradition offence” within the meaning of the 2003 Extradition Act. They also claim that if the conduct is found to be criminal, it should be prosecuted in the UK.

Under English extradition laws, the burden of proof is on the prosecution to show Sarao’s conduct would amount to a crime in the UK.

The defence argued that Sarao’s trading was not central to the flash crash in the US, a prime reason for the request for him to be extradited.

Joel Smith QC, another defence lawyer, said Prof Lawrence Harris, an expert witness on the flash crash who gave evidence through videolink on Thursday, had concluded that Sarao’s trading was not a significant contributor to the crash. “This has been put in to jazz up the request, but it is not right or fair,” he said.

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

The Hounslow-based former bank worker and Brunel University student faces 22 charges including wire fraud and commodities fraud. Sarao denies all the charges.

Mark Summers, representing the US authorities, said there was no doubt that the harm stemming from Sarao’s actions was done in the US and that he should be tried there.

“Protecting the integrity of markets is of great importance,” said Summers, who added that most of the investors affected by the defendant’s trading were investors or intermediaries based in the US.

District judge Quentin Purdy expressed concern for the defendant, who for a second day sat in court with his head down for most of the time.

Lewis reminded the judge that his client had Asperger syndrome and was having treatment for post-traumatic stress disorder.

The judge said that he had a lot of material to sift through and would make a decision on extradition on 23 March.

He told Sarao that his bail terms would be extended but that he would be arrested if he failed to attend court on the assigned day. He initially set a £5m surety as part of Sarao’s bail conditions, which the trader claimed that he was unable to pay. Sarao was released on conditional bail in August after providing a £50,000 surety.

The extradition hearing took place at Westminster magistrates court.

Outside the court Sarao’s solicitor, Richard Egan, asked for the link with the ‘flash crash’ to be downplayed.

“So much of the story has focused on the flash crash. But it is self evident that this link is tenuous.”