If you are hellbent on having a flutter, National Savings & Investments Premium Bonds pays a £1m prize each month with nearly two million other prizes, an a one in 26,000 chance of winning one of them, for each £1 stake (although most people hold far more). The upside is you get unlimited plays and your money back whenever you want it. The downside is that the odds of winning £1m are around one in 40 billion.