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. 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 iTunes downloads and commercial radio airplay across the Global Radio network only, is broadcast on Sunday afternoons from 16:00 to 19:00 on 145 local commercial radio stations across the United Kingdom. The Big Top 40 is not officially regarded by the industry or wider media. There is also a show called "Official KISS Top 40", counting down 40 most played songs on Kiss FM every Sunday 17:00 to 19:00.
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.
The first number one on the UK Singles Chart was "Here in My Heart" by Al Martino for the week ending date 14 November 1952. As of the week ending date 31 May 2018, the UK Singles Chart has had 1338 different number-one hits. The current number-one single is "One Kiss" by Calvin Harris and Dua Lipa.
Before the compilation of sales of records, the music market measured a song's popularity by sales of sheet music. The idea of compiling a chart based on sales originated in the United States, where the music-trade paper Billboard compiled the first chart incorporating sales figures on 20 July 1940. Record charts in the UK began in 1952, when Percy Dickins of the New Musical Express (NME) gathered a pool of 52 stores willing to report sales figures. For the first British chart Dickins telephoned approximately 20 shops, asking for a list of the 10 best-selling songs. These results were then aggregated into a Top 12 chart published in NME on 14 November 1952, with Al Martino's "Here in My Heart" awarded the number-one position. The chart became a successful feature of the periodical; it expanded into a Top 20 format on 1 October 1954, and rival publications began compiling their own charts in 1955. Record Mirror compiled its own Top 10 chart for 22 January 1955; it was based on postal returns from record stores (which were financed by the newspaper). The NME chart was based on a telephone poll. Both charts expanded in size, with Mirror's becoming a Top 20 in October 1955 and NME's becoming a Top 30 in April 1956. Another rival publication, Melody Maker, began compiling its own chart; it telephoned 19 stores to produce a Top 20 for 7 April 1956. It was also the first chart to include Northern Ireland in its sample. Record Mirror began running a Top 5 album chart in July 1956; from November 1958 onwards it was run by NME. In March 1960, Record Retailer began compiling an EP (album) chart and had a Top 50 singles chart. Although NME had the largest circulation of charts in the 1960s and was widely followed, in March 1962 Record Mirror stopped compiling its own chart and published Record Retailer's instead. Retailer began independent auditing in January 1963, and has been used by the UK Singles Chart as the source for number-ones since the week ending 12 March 1960. The choice of Record Retailer as the source has been criticised; however, the chart was unique in listing close to 50 positions for the whole decade. With available lists of which record shops were sampled to compile the charts some shops were subjected to "hyping" but, with Record Retailer being less widely followed than some charts, it was subject to less hyping. Additionally, Retailer was set up by independent record shops and had no funding or affiliation with record companies. However, it had a significantly smaller sample size than some rival charts.