Marks told the IGD Convention the expansion had proved vital in letting the group modernise in the worst economic climate he had ever witnessed.
When asked if, with the benefit of hindsight, he would still have made the deal, Marks replied: "Unequivocally, yes."
He added: "Until five years ago, The Co-op was going down. We called it the co-operative movement, but we didn't co-operate and it didn't move."
Despite The Co-op's success, Marks warned the industry should get used to the brutal economic environment. "This just feels worse than the others," he said. "I don't think I have ever seen consumers as squeezed as this."