(Clarifies that figure in last paragraph refers to 170,000 store workers)

LONDON (Reuters) - Sainsbury's, Britain's second largest supermarket group, will keep all its stores shut on Boxing Day this year, saying it wants to reward staff after a year battling the COVID-19 pandemic.

"The decision to keep all stores shut has been made in recognition of the extraordinary efforts of colleagues throughout a challenging 18 months, since the start of the pandemic," it said on Monday.

Sainsbury's, which employs 170,000 store workers, is one of Britain's biggest private sector employers.

(Reporting by James Davey; editing by Michael Holden)