Hopefully this will help:
http://www.nsandi.com/interest-rates/index.jsp
Premium bonds have an average interest rate of 3.60% - but don't forget that this is tax free - you will be paying tax on Interest from a building society.
To calculate it yourself: Take your winnings (�1000) from your investment (�30,000) which is �29,000. Divide this by your investment (�30,000) and the figure you will have is 0.9667
Subtract this figure from 1 and multiply by 100 - this is the percentage - in this case 3%.
Hope this helps