Birmingham managing director Karren Brady and co-owner David Sullivan were arrested by police investigating alleged corruption in English football, sources said tonight.
The arrests follow last month's raids on Barclays Premier League club Birmingham as part of an ongoing inquiry by the City of London Police's economic crime unit.
Detectives confirmed today they questioned a 59-year-old man and a 39-year-old woman on suspicion of conspiracy to defraud and false accounting.
They were released on bail, police confirmed.
A further seven people, believed to include Portsmouth boss Harry Redknapp, remain on bail in connection with the inquiry.
Officials at St Andrews said tonight they had no knowledge of the arrests.
After last month's raids, the club officials said they were assisting officers in their pursuit of parties with no direct association to the West Midlands club.
Brady, 39, became the UK's youngest managing director when Birmingham City floated on the stock market in 1997.
She is also chairman of Kerrang! magazine and non-executive director of Channel 4, Mothercare and Sport England.
Sullivan, 59, the multi-millionaire proprietor of the Daily Sport and Sunday Sport, co-owns Birmingham with brothers David and Ralph Gold.
Last November officers arrested a series of high-profile figures in the national game in a controversial series of raids.
Among them were believed to be Redknapp, Portsmouth chief executive Peter Storrie, former chairman Milan Mandaric, former player Amdy Faye and agent Willie McKay.
A statement from Birmingham read: '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. By longstanding appointment, they have willingly attended interviews today.
'Birmingham City 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.'