Spend it on paying off credit cards, overdrafts and loans if you have any. The money you spend on interest on such things will be far more than the guaranteed returns on any investments you may make with the money, which strictly speaking is taxable depending on your circumstances.
As people say, if you are a gambler try a flutter on the lottery. For a safer gamble try premium bonds. You get no interest but you may win big time. You can always get your money back. Having said that I've had a few for decades and never won anything.