Some statistics based on the LM Top 20s from May 1970 to October 1975. For the statisticians!
There is an index of songs and artists as well.

A few other thoughts:
These charts can (in theory) be used to work out the top hits of the year. The formula to work out the number of points, as far as I can see, is 1 point for the no 20 song each week, 2 pts for no 19 and so on up to 20 points for the no.1 song each week. However, doing it this way gives a list that doesn't exactly match the official top hits (that were broadcast on the 1st January and also printed in booklet form). It is very close, with the top few positions being the same, but some songs are in different positions from where they end up using the formula above. Some songs were left out altogether, most notable examples being in 1972 when American Pie and Horse With No Name were left out of the top hits.