U.K. Shadow Chancellor John McDonnell has urged the government to investigate Finance Minister Sajid Javid's possible role in financial misconduct.

In a letter to Prime Minister Boris Johnson, the Labour Party politician said there was a need for "public confidence in the suitability and unquestionable integrity of the holders of high public office."

He urged Johnson to look into Javid's relationship to the trading of collateralized debt obligations — a risky financial product widely believed to have catalyzed the financial crisis — while working in a senior role at Deutsche Bank AG.

McDonnell also referred to reports of Javid's involvement in a tax avoidance scheme known as "Dark Blue" and urged the government to look into this.