In court filings, the New York AG said he has uncovered new evidence that Barclays cheated clients and investors, and that top executives knew what was happening.

Schneiderman also said that Barclays has refused to cooperate in his probe, and refused to allow two top trading executives - understood to be William White, head of the bank’s electronic equities trading division, and his number two, David Johnsen, head of product development - he had subpoenaed to submit to questioning.

Alongside the original complaint that Barclays falsely represented to clients the extent of predatory high frequency trading activity in its dark pool, the new suit alleges that the bank's trading alogorithms and smart order routers were specifically designed to funnel more orders through its own marketplace, rather than search for best execution options among other venues.

"Barclays' smart order router was biased in favor of its own dark pool, regardless of whether an order was likely to be filled there, and secondarily to other venues based on whether those venues were profitable for Barclays," states the suit. "When a detailed analysis of Barclays' order routing practices was conducted for a major institutional investor (that manages money for thousands of ordinary investors, including many in New York) showing that Barclays was routing and executing the vast bulk of this client's sampled orders to Barclays' own dark pool, senior Barclays executives directed that a written presentation to that client be falsified to mask Barclays' biased order routing practices."

Barclays has refuted the allegations.

“The amended complaint merely repackages the same flawed arguments that were in the original complaint,” Barclays spokesman Mark Lane told Bloomberg. “While we continue to seek to cooperate with the New York Attorney General in this matter, we will continue to defend vigorously against these allegations.”