The superstores are currently owned by British Land and leased to Sainsbury’s for 20 years.
A single Waitrose store will also be included in the JV, bringing the total number of stores to 39.
Sainsbury’s said: “Creation of this JV unlocks the opportunity to significantly develop these stores and deliver an improved customer offer.
“The JV will seek to maximise the full potential of these development opportunities, including extending up to 25 sites by an estimated 500,000sq ft of net selling area.
“Sainsbury’s will benefit from both the enhanced trading performance of the extensions as well as retaining a share of the increased property value.”
The JV is for an initial period of 10 years.
Justin King, chief executive, said: “This venture is an excellent opportunity for Sainsbury’s to increase our interest in the future extension and development of many of our most important stores.
“This will enable us to enhance the customer offer, increasing both the trading and property value of these assets.”
Stephen Hester, chief executive, British Land, said: “Today’s agreement more closely aligns the interests of property owner and retailer to deliver value to shareholders in both companies.
“It acts as a catalyst to increase capital value by improving, through extensions and developments, the Sainsbury Stores.”
Also today, Sainsbury’s announced like-for-like sales up by 4.1% for the fourth quarter of its financial year.
