Labor is demanding an investigation into whether the final report of the banking royal commission was leaked from inside the government, delivering a $22 million windfall to investors.

The half a billion dollar plunge on the banks just hours before the public release of the report has raised eyebrows that news the report was softer than expected on the banks was leaked.

Treasurer Josh Frydenberg “guaranteed” the royal commission’s final report would not leak while the government declined to release the document for three days.

Labor’s shadow financial services spokesman Clare O’Neil has now formally asked the question, citing a report in The New Daily by journalist Michael Pascoe …