Sainsbury’s has confirmed plans to merge with Asda, which is currently owned by US supermarket giant Walmart.
The supermarkets said that grocery prices would fall in both chains as a result of the merger.
Sainsbury’s chief executive Mike Coupe said the deal would lead to no store closures and no job losses in stores.
The combination of the UK’s second and third largest supermarkets would create a giant, representing nearly £1 in every £3 spent on groceries.
“There will be be no store closures,” Mr Coupe told the BBC’s Today programme.
“There’s been a bit of commentary over the weekend where people have been alluding to the fact that the only way of making this happen is by closing stores – that is not true.
“The stores will continue to trade and of course that’s where the vast majority of people employed by both companies actually work.”
Mr Coupe – who will lead the new combined group – said he believed the two supermarkets were “the best possible fit”.
“It will enable us to bring prices down, to improve quality, to improve ranges and to bring the power of Walmart in the form of buying of general merchandise and in the form of their systems and investments to the UK,” he said.
Walmart will retain a 42% stake in the newly-merged company following the deal. Sainsbury’s and Asda said they would have a close relationship with Walmart as a strategic partner.
The supermarkets said they expected to be able to lower prices “by around 10% on many of the products customers buy regularly”.
Given the size of the two chains, the deal is expected to need approval from the Competition and Markets Authority (CMA).
At the weekend, Liberal Democrat leader Sir Vince Cable said the CMA should force the companies to sell off stores if the merger meant the new giant was dominant in a particular area. He said the move risked creating “even more concentrated local monopolies”.
Latest figures show Tesco has a 25% grocery market share, while Sainsbury’s has 13.8% and Asda has 12.9%.
Mr Coupe told the BBC he expected the deal to be completed by the autumn of 2019.