It is inevitable that, statistically, you will win less often (for the same number of Bonds) when interest rates are low (as they are now). This is because the Treasury adjust the quantity of prizes doled out so it matches the total amount they offer as prize payouts, according to the underlaying interest rates. Since the Treasury want to maintain the headline-grabbing £1m montly top prize, the quantity of the smaller prizes have been scaled back dramatically since interest rates were at (say) 5% p.a.