The Co-operative Bank's former chairman Paul Flowers has apologised for his "stupid and wrong" behaviour and said he is seeking professional help after a video was published showing the Methodist minister handing over money to buy hard drugs.

The footage showed Flowers counting out £300 in cash and asking if he could also get hold of ketamine. The Mail on Sunday said a friend of Flowers handed over the footage, purportedly recorded days after the former Co-operative Bank chairman gave testimony to the Treasury select committee over the bank's £700m in losses and its abandoned bid to buy branches of the bailed-out Lloyds Bank.

Stuart Davies handed over the video and a series of incriminating text messages after becoming "disgusted by the hypocrisy" of a man who had chaired the anti-drugs charity Lifeline and written columns about the evils of drug use, the Mail on Sunday said.

After being confronted with the material, Flowers, 63, referred to the pressures of his job and dealing with a family bereavement.

"This year has been incredibly difficult, with a death in the family and the pressures of my role with the Co-operative Bank," he said. "At the lowest point in this terrible period I did things that were stupid and wrong. I am sorry for this and I am seeking professional help and apologise to all I have hurt or failed by my actions."

Davies also handed over text messages purporting to be from Flowers. One said: "I was 'grilled' by the Treasury select committee yesterday and afterwards came to Manchester to get wasted with friends." In others he said he was on "ket" and had the club drug GHB. Davies said he smoked cannabis with Flowers and witnessed him smoking crack cocaine.

The Co-operative Bank said it had no comment, while the Methodist church said a thorough investigation would take place.

"We expect high standards of our ministers and we have procedures in place for when ministers fail to meet those standards.

"Paul is suspended from duties for a period of three weeks, pending investigations, and will not be available to carry out any ministerial work. We will also work with the police if they feel a crime has been committed."

On 7 November, Flowers tried to spread the blame for the bank's woes, telling the select committee that politicians had actively encouraged the Co-op Bank's expansion spree involving an ill-fated attempt to buy 631 branches from the Lloyds Banking Group.

The bank also disastrously took over the Britannia building society, a deal that brought with it a raft of bad loans.

Flowers said he had resigned as chairman in June 2013 to take responsibility for a £1.5bn capital shortfall that left the Co-op group having to demutualise the 100-year-old bank and hand a 70% share in the British institution to a group of bondholders involving US hedge funds.