The National Savings and Investments Agency allows Premium Bond holders to enter their holder's numbers on the NS&I website to see if they have won a recent or unclaimed draw. Premium Bond holders can also check their numbers by phone or through the mail.
According to the NS&I, as of June 2013, over 898,000 Premium Bond prizes remained unclaimed. There is no time limit to claim a prize, but if a prize has not been redeemed 18 months after a prize draw, it is considered unclaimed.
Premium Bonds are a monthly lottery sponsored by the United Kingdom's government and first introduced in 1957.