PETER Marks, chief executive of Co-operative Group, said he is to retire next May but that his departure would not derail the integration of Lloyds TSB Scotland into the mutual.

Mr Marks is leaving just months before the launch of Co-operative's assault on the Scottish banking market following its acquisition of 189 branches north of the Border to add to the four it currently operates.

The group is already the fourth biggest retailer in Scotland, with 370 food stores stretching from Shetland to the Borders.

Mr Marks, who will be 63 when he leaves, told The Herald that following Co-operative's £750 million acquisition of Lloyds's Verde portfolio, which is due to complete by November 2013, integration of the 632 branches UK-wide would be a three-to-five year project.

"I think I have done enough," he added.

Asked if his move would raise doubts about Co-operative's ability to implement the integration, he said: "I do not think so. We have a team that have exceptional expertise in integration. We know what we are doing."

He noted that in recent years the group has brought Somerfield into its retail arm and merged Britannia building society with its bank.

He added that Verde chief executive Paul Pester, who will run the combined business on merger, is a "high quality banking executive with significant integration experience".

Mr Marks highlighted the importance of the Lloyds deal to its Scottish business, which will have the country's third biggest bank branch network, operating under the TSB name.

"We have got a great following in Scotland, we always have had," he said.

"Now it is going to be even bigger with the TSB brand coming back and a bigger presence in the banking world. That was really important to us."

Mr Marks said he had always intended to retire at 63 but held off announcing anything in case it jeopardised the Lloyds deal.

When Mr Marks steps down as chief executive he will have served in the role for six years and spent 45 years with the wider Co-operative movement. He said his proudest achievement was the consolidation of the Co-operative movement, including the 2007 merger of the Co-operative Group with United Co-operatives, which he had previously led. He said: "It delivered a significant increase in profit and we then had the confidence to invest, which led to Somerfield, Britannia and now Verde."

He added: "If ever there was a time for mutualism to make a real comeback, now is it. You only have to look back at banking over the past three or four years. People have lost trust in the plc model, particularly in financial services."

Mr Marks said he intends to use his retirement to travel and spend more time with his family but does not intend to leave business life entirely.

The Co-operative said its board will now start the search for a successor and will consider internal and external candidates.

Len Wardle, chairman of the Co-operative Group, said: "Peter has done a truly outstanding job for the Co-operative Group.

"As a result, the Co-operative Group is better placed than ever before to do what it does best – offering a real alternative on the high street with a unique focus on ethical business under a brand which, more than any other, stands for trust."

Co-operative is the fourth largest food retailer in Scotland, and the group employs 11,000 people north of the Border.

The mutual, which has 475,000 Co-operative Group members in Scotland, has continued to grow its presence, acquiring the 28-strong David Sands chain this year. The stores will be reopened as Co-operative Foodstores.

It also has 120 funeral homes, 60 pharmacies, a new £35m regional distribution centre at Newhouse, near Glasgow, three farms and two packhouses.