J Sainsbury, the supermarket chain, is in advanced talks to sell a portfolio of prime shopping sites to a London-listed property investor for around £500m.

Sky News has learned that LXi REIT, which has a market value of around £2.5billion, is close to agreeing a deal to acquire the freeholds of nearly 20 Sainsbury’s stores, which the grocer will then intend to rent.

A property industry source said on Tuesday evening that LXi would likely seek to raise hundreds of millions of pounds of equity to fund the acquisition, with some of the consideration also including an unspecified amount of debt.

If confirmed, the deal would come months after it emerged Sainsbury’s was considering selling the portfolio.

A number of other parties have reportedly expressed interest in acquiring it.

Supermarket groups are under pressure from investors to improve the efficiency of their balance sheets, with Asda and Wm Morrison having been acquired by new owners in the past two years.

LXi REIT has been active this year, agreeing to a takeover of its peer Secure Income REIT several months ago.

Among the major assets it owns are properties that are part of Merlin Entertainment, the group behind the theme parks Alton Towers, Legoland and Thorpe Park.

It invests in commercial real estate assets which benefit from long leases, generally with duration of several decades, and is a member of the FTSE-250 index.

Both LXI and Sainsbury’s declined to comment.