[tialaramex]

The British government owns lots of banks, one of them, the National Savings and Investment Bank has a product that is almost this (but not secret), named 'Premium Bonds'.

You buy bonds, and like a lottery ticket they might randomly win a prize in a draw. But because it's a bank not a lottery the bonds themselves never go away if you don't win, it's basically a savings account except instead of boring percentage interest you randomly win prizes.