The charts we use from November 1952 onwards are compiled by the Official Charts Company which produces the UK Singles Chart for the music industry, including the BBC. Their information can differ from that shown in reference guides such as The Guinness Book of British Hit Singles (now The Virgin Book of British Hit Singles). We explain this more fully here and you can find even more detail on the history of the charts on the Official Charts Company website.
The official UK pop charts based on record sales did not start until 14th November 1952. For earlier dates than this, we have used the weekly pop chart based on the sales of sheet music, which was published by Melody Maker and broadcast by Radio Luxembourg from May 1947. (Sheet music outsold records in the United Kingdom until the early 1950s.)