Mike Lazenby, dubbed Maverick Mike for shaking up a traditional building society and turning it into the fastest-growing in the UK, is to quit after 11 years.

The shock decision came just days after he masterminded the controversial transformation of the former Kent Reliance Building Society into OneSavingsBank Plc, based in Sun Pier, Chatham.

Mr Lazenby was in India when his departure was announced. He will leave with a payoff thought to be equivalent to a year's salary of £385,000. Finance director Bob Scruton takes over as interim CEO until a successor is found.

The bank is owned jointly by private equity investor J C Flowers, which injected £50m into the business, and a new mutual organisation Kent Reliance Provident Society.

In a prepared statement, Mr Lazenby said: "I am very proud of the strong reputation we have built in retail financial services, and it has been a privilege to work with such a talented team.

"I have no doubt that OneSavings Bank will go from strength to strength whilst retaining its mutual ethos at the heart of the business."

Bank chairman Malcolm McCaig said: "Mike is a passionate supporter of mutuality, and had the foresight to recognise the need for Kent Reliance to seek a partner to preserve its mutual ethos and further develop its franchise.

"He played a key part in the creation of OneSavings Bank, and, in doing so, has helped protect the interests of members as part of a bigger, better capitalised and competitive player in the financial services sector.

"Having achieved this, Mike and the Board have agreed that the time is right for him to step down from his position as CEO. The Board would like to thank him for all he has done for KRPS and OneSavings Bank, and for his role in creating such a strong foundation for future growth. We wish him well in his future endeavours."