The deal means Glasgow-based Filshill, which owns the Keystore convenience store brand, will supply the six food stores owned by the Clydebank Co-op. It comes after Keystore and the group launched their first jointly branded convenience store in Glasgow's Knightswood area in September.
Robert Sider, chief executive of Clydebank Co-operative, said: "We have enjoyed an excellent relationship with CRTG but we are operating in an extremely challenging marketplace and believe our stores will be in a much stronger position going forward if we have more flexibility when it comes to promotions and sourcing products.
"Indeed, our jointly branded Clydebank Co-operative Society/KeyStore in Knightswood is performing ahead of targets, confirming that the wider product choice and access to more local and Scottish lines is striking a chord with consumers."
Simon Hannah, managing director of JW Filshill, described the partnership as one "we're very excited about".