Flowers, dubbed the Crystal Methodist, appeared before Leeds Magistrates' Court yesterday, where he pleaded guilty to two counts of possession of Class A drugs - cocaine and crystal meth - and one count of possession of the Class C drug ketamine.
The charges flowed from secret video footage of him which showed him handing over £300 in cash for the drugs in the West Yorkshire city in November last year.
District Judge David Kitson was told that Flowers had used cocaine for about 18 months but had little previous experience of the other two drugs. Mr Kitson fined the 63-year-old minister £400 and ordered him to pay £125 in costs.
Flowers said nothing as he left court. Earlier, he arrived before the building opened and had to endure five minutes of flash photography as he waited on the pavement.
His court appearance came as the Co-op was urged to back radical reforms that will sweep away the "dysfunctional" board which presided over the mutual's near-collapse.
Former City minister Lord Myners set out his plans for a "plc and beyond" structure by replacing the existing 20-strong board of representatives from the co-operative movement with professionally trained directors.
His proposals will be put to the vote at the Co-op's AGM in Manchester on May 17, but the peer fears that many traditionalists are "still stuck in denial" over the failings of the Co-op, which reported an annual loss of £2.5 billion last month.
Despite its membership of around eight million and 90,000 workforce, Lord Myners said that whether his report is accepted will depend on the votes of about 100 "elected democrats" who sit on regional boards.
Lord Myners said: "I have no doubt that the Co-operative Group can reverse a decline that started over 50 years ago. But I am less confident that it will choose to do so."
Ursula Lidbetter, chairman of the Co-operative Group, said a resolution containing the four key principles on reform will be put to members at the AGM.
She added that the board of the group has made clear its "commitment to far-reaching and fundamental reform of our governance".