Sainsbury's and Asda will not be allowed to merge due to concerns over prices and customer shopping experience, the competition watchdog has ruled.
Sainsbury's boss Mike Coupe said the Competition and Markets Authority (CMA) was "effectively taking £1bn out of customers' pockets", but conceded it would not appeal the decision.
"The CMA's conclusion that we would increase prices post-merger ignores the dynamic and highly competitive nature of the UK grocery market," he added.
The merger would've created the UK's biggest supermarket, which both companies stressed would have allowed them to cut prices. But the CMA told the BBC: "It would reduce competition in supermarkets and online grocery shopping and at the companies' petrol stations.
"We think that is likely to lead to higher prices or other changes which would be unwelcome to shoppers, such as longer check out queues."