Midcounties Co-operative Society has purchased the 10-store independent c-store chain Rusts for an undisclosed sum - the second Top 50 independent retailer it has bought in nine months.
Rusts founder and chairman John Emeny said his retirement was the main reason for the sale, but an inability to secure sites for expansion had also prompted him to exit the business.
Competition from Tesco, Sainsbury's and Marks & Spencer for sites had made it much more difficult for him to find places for new stores, he said.
"It is a good time for me to leave," he added. "I am pleased the Co-op has bought Rusts because they treat their staff well and their concept of neighbourhood retailing is in line with mine."
A spokesman for Midcounties, which in January acquired the Stars News Shops chain, said: "It's very much business as usual for staff and customers and we have no operational changes planned at this stage. We are looking forward to settling the stores into our estate."
Rusts ranked 42nd in The Top 50 with a turnover of £11.8m and a pre-tax profit of £104,000 last year.
Emeny, who has worked in the industry for 60 years and established Rusts with just £25,000 and two stores in 1978, said he was hoping to open his own caravan park on the south coast of England and would even consider running a small convenience store on the site.