Graham Bennett is to step down as chief executive of Southern Co-operatives after 25 years at the helm of the UK's fifth-largest co-op.

Bennett, who has worked at Southern Co-op for 30 years, will step down in October. He will be replaced by Mark Smith who becomes CEO designate from 1 June.

During the transition period Bennett will remain at the company to ensure a smooth handover. He will also continue to be a board director of The Co-operative Group and chairman of The Co-operative Bank.

Southern Co-op operates more than 100 food stores across Hampshire, Berkshire, Dorset, the Isle of Wight, West Sussex and Wiltshire. Under Bennett's leadership, the society has introduced business community wardens to the streets of Portsmouth in a bid to fight low-level crime and banished plastic carrier bags from a number of its food stores.

Earlier this month the society reported like-for-like sales growth of 7.6% for the year to 26 January. Group pre-tax profit rose 22% to £10m on group sales up 10.4% to £198.1m.

"It is particularly pleasing to see the benefits of our investment programme reflected in our latest results, and I am delighted to be handing the society on in such good shape," said Bennett.

Smith joined Southern Co-op in 2005 as deputy chief executive . He is also a trustee of the Southern Co-operatives Foundation which makes donations to charities, community groups and organisations in the society's trading area.

"I am certain this will be a successful and seamless transition that builds on our recent strong trading performance," said chairman David Blowe.

Smith added: "I am thrilled to be taking over the leadership of the society from a position of financial strength and with such a dedicated team of people."