The closure of 79 Kwik Save stores will be completed by today as the supermarket chain battles for survival.
Trade unions warn hundreds of jobs will be lost in the closures, which the firm says are needed to secure its future.
The company said in a brief statement: "It is with regret that Kwik Save has had to make this difficult decision. However, in order to enable the business to succeed, the Kwik Save management team has had to announce these cutbacks to secure the future of the business.
"Kwik Save would like to thank all of its staff affected by this regrettable situation for their commitment to the company over the years."
A total of 147 stores will remain open after the closures.
A spokesman for the shopworkers' union Usdaw said: "This is a huge number of closures which will affect many workers.
"We will be seeing an urgent meeting with the company to clarify what redundancy package workers can expect as well as discussing the long term future of the business."
The Kwik Save store in Wellington, Shropshire, closed yesterday with the loss of up to 12 jobs. Customers turning up to the supermarket found a note at the premises announcing its closure.
There had been speculation in recent days that the firm was facing a new cash crisis after receiving a £50 million rescue package in February.
Late last week Arla Foods stopped delivering milk to the grocery chain, citing "payment problems", and unconfirmed reports suggested Kwik Save's bread supplies had also been stopped at a number of stores in the past few days.Reuse content