The British television show Dragon’s Den originally aired on BBC Two.
BBC Two was the programme’s launch channel when the series began in January 2005. Its format combines business advice, negotiation and entertainment: entrepreneurs present proposals to a panel of investors and seek funding in exchange for an ownership share.
The programme’s success made Dragon’s Den one of the BBC’s best-known factual-entertainment brands. Although it has remained associated with the BBC, viewers sometimes mix it up with ITV’s The X Factor or with the American business series Shark Tank, which uses a related international format.
BBC Two is therefore the specific answer for the original UK broadcaster. This is different from asking which channel carried a particular repeat, special or regional broadcast.