Co-owner Sullivan and managing director Brady were reportedly questioned about alleged false accounting and conspiracy to defraud. "By longstanding appointment, they have willingly attended interviews today.
A statement on the club's official website reads: "David Sullivan and Karren Brady, on behalf of Birmingham City Football Club, were invited to co-operate with a City of London Police investigation and have happily done so.
"Birmingham City football Club is fully committed to helping the Police with their enquiries.
"For the avoidance of doubt, no charges have been brought.
"We have been requested by the Police not to comment further whilst their enquiry is ongoing."