The two firms hope the partnership will reduce the cost of own-label goods and give them a competitive edge, but Spar group trading director Peter Miller said it would continue with its own specifications if it believed a product was particularly important to shoppers.
He said: "We will migrate to single spec where we can, but we would need to be offered a particularly spectacular own-label cola to move away from Spar American Cola, for example, which is one of our biggest brands and a high-quality product. However, I don't think anyone would lose any sleep if we changed our tinned tomatoes."
Miller added that the alliance should also enable Spar to extend its 1,000-strong own-label range.
Under terms of the buying alliance, both organisations will keep control of their own branding, promotions and marketing, while the Co-operative Retail Trading Group will manage the initiative.
Own-brand products that will be bought jointly are: paper, foil and wraps, cooking oils, olive oils, fats, pasta, sauces and pickles, canned fruit, fruit juice, frozen foods, carbonates, household and laundry, spirits, water, canned vegetables and eggs. The first jointly sourced products are set to appear on shelf early next year and other categories could be added if the initiative proves successful.
Co-operative Group chief executive of food retail Guy McCracken said that it made good commercial sense to build scale and improve its position when there was increasing consolidation in the sector.
Spar managing director Jerry Marwood added: "This buying partnership is good news for Spar as it represents a positive move that will help us secure our future and allow us to compete on a more equitable footing with the multiples."