The actress, best known for quirky roles in shows such as Jonathan Creek and Men Behaving Badly, beings shooting her new role in BlueMurder next month.
He accused Ed Balls, a former adviser to Gordon Brown and now shadow chancellor, of "sucking up" to the banks and letting them get away with "blue murder" during Labour's time in power.
He arrived wearing a blue suit and a tie before prosecutors began outlining their case - expected to be a charge of premeditated murder that he will deny.