A Merrill Lynch currency trader has been suspended after racking up more than $400m in undisclosed losses in recent months, raising further questions about the financial health of the investment bank bought by Bank of America last September.

Merrill is poring over the books of Alexis Stenfors, a London currency trader, who was suspended after Norwegian and Swedish currency trades went wrong, according to people familiar with the situation. Merrill is in talks with UK regulators after uncovering what it called a trading “irregularity” in London.