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However, it is reported that those who automatically reinvested prize winnings into Premium Bonds are not affected by the glitch.
Premium Bond holders can check if their numbers were drawn using the NS&I prize checker tool online.
An NS&I spokesperson said: "Following an update to NS&I’s systems in mid-July, it was discovered that, when customers were investing in NS&I products, the incorrect date for the sale was being applied to the transaction in some cases. NS&I apologises to all customers affected."
"Retrospective prize checks have been run on the affected Bonds, and customers will be notified in writing by NS&I of any prize wins."