More than a million people have failed to pick up their Premium Bond prizes, leaving nearly £54 million unclaimed.
They include a £10,000 prize won in the February 2001 draw by a man in Staffordshire who holds just £20 in Premium Bonds.
And one Essex woman is owed £25,000 from a draw from May 2014.
In Norwich, there are 5,927 unclaimed prizes worth more than £228,000 - including one owed to a woman with just £2 invested. The highest value unclaimed prize in the city is worth £1,000, and the oldest dates back to December 1971 - a £25 prize belonging to a man holding jus £3 in Premium Bonds.
In Bristol meanwhile, there are 7,991 unclaimed prizes worth a total of over £321,000. The highest-value unclaimed prize is £1,000, won in the February 2000 draw. The oldest unclaimed prize in Bristol is £25 and was won back in August 1964, by a man with a £10,011 investment.
"Prizes often become unclaimed as a result of people moving house, or forgetting that Bonds have been bought for them as a child, or executors are unaware the Bonds are held when someone dies," says Jill Waters, operations manager for National Savings & Investments (NS&I).
There's no deadline to claim.
NS&I is urging Premium Bonds holders to avoid missing out by registering to have any prizes paid directly into their bank account and to receive a notification by email.
"We're always striving to offer customers what they want and have now made it easier to manage their Bonds through our online and phone service, and we are delighted that over a million of our customers are now choosing to have their prizes paid directly into their nominated account," says Waters.
More than 21 million people - around a third of British adults - hold Premium Bonds, worth a total of over £63 billion. However, earlier this year, a Which? survey revealed that 10% of people believe they may have lost track of their holdings.
If you think you might have won, you can check your numbers here.