You could consider Premium Bonds. You can invest up to �30,000 and you can easily get your money back (although not instantly). Any winnings are tax free and each month there are two �1m prizes and others ranging from �50 to �100k.
You do not receive any interest on your investment, though - just the chance to win.
Here is the prize breakdown from June:
Prize band Prize value Number of prizes
Higher value
7% of prize fund �1 million 2
�100,000 7
�50,000 13
�25,000 26
�10,000 66
�5,000 133
Medium value
6% of prize fund �1,000 1,825
�500 5,475
Lower value
87% of prize fund �100 41,882
�50 1,239,935
Total value �76.07 million 1,289,364
Otherwise, put it all on Laughing Boy in the 3.30 at Ascot....