The biggest unclaimed prizes are two worth £100,000, owed to a woman in London, and another from Manchester.

Over a third of the UK population have invested over £45bn in Premium Bonds, and every eligible Bond is entered into the monthly prize draw. Investors forgo interest to have the chance to win tax-free prizes.

Premium Bond prizes usually go unclaimed when people forget to tell NS&I about changes in contact details.

There is no time limit for claiming prizes and each unclaimed prize is held until the rightful winner can be tracked down.

The oldest unclaimed prize dates back to November 1957 where a male in South Yorkshire has a prize to the sum of £25 waiting to be claimed.

Jill Waters, NS&I’s operations manager, said: “It is likely that the winner of the £100,000 prize is unaware or she has forgotten that she has Premium Bonds – the lucky winner has just £25 invested. 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.”