There is no such thing as a £500 or £100 premium bond. Each premium bond is £1 (although the minimum purchase is £25 or 25 bonds).For 23 years I had two £500 Premium Bonds which never won anything at all. Two years ago I sold them and took out ten £100 Premium Bonds instead. Same amount of money, but using more lower value bonds rather than higher value bonds. In the two years since doing that, I have had two £50 wins. Coincidence or not? I have no idea.