Perhaps my post was a little vague. I may bot have written in a clear enough way, but Premium bonds are fully and completely refundable. If you buy £1000 worth, no matter how long you leave them therr, you get £1000 back- plus all those chances of winning monthly. So by reinvesting all winning, im increasing my chances of a "big" win, but all my investment completely safe. It takes about a week to withdraw all your money.