Thorntons is to close up to 180 stores over the next three years following a strategic review of its business.
The chocolate maker, which gave a profit warning in May, said "a minimum" of 120 shops would shut, with the possibility of an extra 60 closures.
Thorntons said the outlets that will be closed are among the 364 stores directly owned and run by the company.
It said it hoped to replace them with franchised stores "in the majority of locations".
Thorntons currently has 227 shops run by franchisees.
Shares in the company were down 5% in London trading.
The company added that it would continue to expand its commercial division, which sells Thornton-branded chocolate via supermarkets and other retailers.
In addition, it aims to continue to grow sales via its website.
Thorntons also said it wanted its sales to become less dependent on seasonal events such as Easter and Christmas.
To do this, it is introducing a new range of smaller chocolate gift products for birthday presents, anniversary gifts or thank you presents.
Chief executive Jonathan Hart said: "Our goal is to refocus the business across all channels, and seek to deliver industry competitive results over the next three to five years.
"Although we see the prospect of weakness in High Street footfall and consumer sentiment continuing, I am confident that this strategy is right."
Thorntons' warning of continuing weak trading comes as a number of retailers are struggling against a backdrop of lower consumer spending.
Over the past week, fashion chain Jane Norman and home fittings company Homeform have both gone into administration.
In addition, Habitat announced that all but three of its UK stores had been put into administration.
The most recent official figures showed that UK retail sales fell 1.4% in May.