Waitrose managing director Rob Collins said his head beat his heart as he emphatically backed the new management structure at John Lewis Partnership, which will result in his departure.

He also quashed recent speculation that Waitrose could be sold by the John Lewis Partnership.

Collins, who has spent 26 years at the partnership after joining as a graduate trainee in 1993 and led Waitrose for the last four years, will depart in January after deciding that “there isn’t a role in the new structure that I believe is right for me”.

He told Retail Week he fully backed the new arrangement, which brings the management of grocer Waitrose and John Lewis department stores together under a single team reporting to new chair Sharon White.

The roles of managing director and the operating boards of each will be abandoned as the retailer seeks to create one business and the associated synergies.

Collins said: “It was heart and head. My heart says I’ve got one of the best jobs in retail running Waitrose. My head says we’re doing what’s in the best interests of the partnership going forward. I’ve said to everybody that I’m absolutely convinced this is the right step for the partnership.

“I start with the customer and increasingly we see the majority of sales from the customers of both brands. The two together are more competitive than on their own.”

None of the new partnership executive team so far have come from Waitrose, prompting concern about its ability to oversee a complex food retail business.

But Collins maintained: “The reality is if you look below the executive team you see a deep seam of Waitrose experience.” He said, for instance, that commercial director Rupert Thomas would be leading all food buying across the partnership.

There has recently been media speculation that Waitrose could be sold and Amazon was reported to be a potential buyer.

Asked if Waitrose would remain as part of the partnership for the foreseeable future Collins replied: “Categorically yes. Waitrose is a great part of the partnership and central to making the partnership a success.”

Collins has not decided what he might do next. He added: “I want to go on to do other things but the number one priority for the next four months is to set Sharon up for success.”