Barclays has instructed US law firm trio Sullivan & Cromwell, Boies Schiller & Flexner and WilmerHale to defend it from a New York lawsuit alleging the bank misled investors about its high frequency trading operations.

On 25 June the New York Attorney General, Eric Schneiderman filed the suit against the lender, accusing it of a "systematic pattern of fraud and deceit" within its so-called 'dark pool' trading division.

In a filing yesterday (24 July) Barclays rejected the allegations, called for the suit's dismissal, and argued that the Attorney General did not identify fraud, victims or any harm. The bank says the complaint is based on "clear and substantial factual errors".

The filing also shows the bank has appointed Sullivan & Cromwell as its lead defence counsel, with litigation partners David Braff, Jeffery Scott and Matthew Schwartz in New York and Washington DC-based partner Brent McIntosh all named in the response.

Sullivan & Cromwell's litigation team is also advising the bank over allegations that Barclays and more than a dozen other banks rigged rates in the foreign exchange market. The white shoe firm has also advised the bank on Libor issues.

Litigation boutique Boies Schiller, which has also defended Barclays in numerous lawsuits filed after the bank's $453m Libor settlement, has also been appointed for the dark pool complaint, with firm founding partner Jonathan Schiller again being drafted in alongside fellow New York litigation partner Christopher Duffy.

Boies, whose City launch last year was partly driven by a growing caseload for the bank, also took a role for Barclays on Anthony Salz's independent review of Barclays' business practices in 2013.

Both Boies and Sullivan & Cromwell were both appointed to Barclays' 19-strong 'preferred' list of law firms at the beginning of this month, in a sign of UK banks' growing requirement to build relationships with major US litigation and financial regulatory outfits.

Barclays is also working with Washington DC-based WilmerHale partner Matthew Martens, who joined the firm last year from the Securities and Exchange Commission (SEC), where he was chief litigation counsel for the division of enforcement.

WilmerHale was not one of the firms listed as 'preferred' in Barclays' review, though the bank said following its recent review it would continue work with around 70% of the 100-plus firms that were appointed to its panel in 2011.

Commenting on the dark pool case, a bank spokesperson said: "Barclays works closely with its regulators in all jurisdictions and will continue to cooperate with the New York Attorney General. However, we do not believe that this suit is justified, and we have a duty to our shareholders, clients and staff to defend our position."

In response to Barclays' filing, the Attorney General said: "We are confident that a judge will reject this motion and allow us to prove these disturbing allegations in Court."