Morrison's in Cambourne has been ordered to make changes after going ahead with a refurbishment without planning permission.
Planners from South Cambs District Council have refused the retrospective application, saying the supermarket's application would make the store an overbearing presence on the High Street. Planners say this undermines the council's long-term vision to create a diverse hub for Cambridgeshire's newest community.
The supermarket's original planning permission limited the range of goods it could sell to allow other shops to be successful around it and the floor area in the shop that could be used to sell products from was limited to 2,800 square metres. The latest retrospective planning application seeks permission for the increase in the size of the floor space being used to 3,200 square metres.
The council will now issue the store with a breach of its planning condition as the store made the changes before securing permission. The breach of permission notice will give Morrison's a set period to reverse the changes.