Derek Kilkenny-Blake has kept his Premium Bond in a filing cabinet at his home in Gloucestershire for more than half a century. Originally bought for him as a christening present by his grandfather in 1961, Mr Kilkenny-Blake’s National Savings and Investments (NS&I) certificate has been dutifully preserved for 62 years. Sadly for Mr Kilkenny-Blake, now 63, the bond has yet to return a prize. “I have always kept my name up to date on the register, but I haven’t won anything,” he says. “It’s a lottery I suppose, and I have friends who win regularly, but I suppose I am just unlucky.” Premium bonds function atypically to standard savings accounts or cash Isas. Rather than earning interest, every month NS&I uses its Electronic Random Number Indicator Equipment (affectionately called ERNIE), to award random bond-holders prizes between £25 and £1 million. The odds are adjusted every year to account for the ballooning number of bondholders. NS&I says a typical £25 investment (the minimum buy-in) has a 1 in 840 chance of winning the minimum prize every month. The chances of winning one of the two £1m prizes with a £25 investment are roughly one in two-and-a-half billion. Each £1 Premium Bond,...