Official Singles Chart

The UK Singles Chart (currently entitled Official Singles Chart) is compiled by the Official Charts Company (OCC), on behalf of the British record industry, listing the top-selling singles in the United Kingdom, based upon physical sales, paid-for downloads and streaming. To be eligible for the chart, a single is currently defined by the Official Charts Company (OCC) as either a 'single bundle' having no more than four tracks and not lasting longer than 25 minutes or one digital audio track not longer than 15 minutes with a minimum sale price of 40 pence. The rules have changed many times as technology has developed, the most notable being the inclusion of digital downloads in 2005 and streaming in July 2014.

The OCC website contains the Top 100 chart. Some media outlets only list the Top 40 (such as the BBC) or the Top 75 (such as Music Week magazine) of this list. Around 6,500 British retail outlets contribute sales data, as well as most UK online digital-download stores. Unlike charts in the United States, no airplay statistics are used for the official UK Singles Chart. The chart week runs from 00:01 Friday to midnight Thursday, with most UK physical and digital singles being released on Fridays. From 3 August 1969 until 5 July 2015, the chart week ran from 00:01 Sunday to midnight Saturday.

The Top 40 chart is first issued on Friday afternoons by BBC Radio 1 as The Official Chart from 16:00 to 17:45, before the full Official Singles Chart Top 100 is posted on the Official Charts Company's website. A rival chart show, The Vodafone Big Top 40, is based on downloads and commercial radio airplay and is broadcast on Sunday afternoons from 16:00 to 19:00 on 145 local commercial radio stations across the United Kingdom.

The UK Singles Chart began to be compiled in 1952. According to the Official Charts Company's statistics, as of 1 July 2012, 1,200 singles have topped the UK Singles Chart. The precise number of chart-toppers is debatable due to the profusion of competing charts from the 1950s to the 1980s, but the usual list used is that endorsed by the Guinness Book of British Hit Singles and subsequently adopted by the Official Charts Company. The company regards a selected period of the New Musical Express chart (only from 1952 to 1960) and the Record Retailer chart from 1960 to 1969 as predecessors for the period prior to 11 February 1969, where multiples of competing charts (none official) coexisted side by side. For example, the BBC compiled its own chart based on an average of the music papers of the time; many songs announced as having reached number one on BBC Radio and Top of the Pops prior to 1969 are not listed as chart-toppers according to the legacy criteria of the Charts Company.

...
Wikipedia