Manchester became the main filming location for Dragon's Den after production moved from London.
The programme was originally filmed in London, but production later moved to Manchester. The move connected the show with the North of England and helped make the Den part of the region's television-production landscape. The programme has also been associated with MediaCityUK in nearby Salford, an important production hub.
Manchester and Salford are closely linked geographically, which can create confusion in short descriptions of the location. The city generally identified with the production move is Manchester, while MediaCityUK itself is in Salford.
Filming location is separate from the location of a contestant's business. Entrepreneurs travel from across the United Kingdom and may operate in entirely different cities. The answer concerns where the television production was based, not where any particular pitch originated.