Salford is home to the BBC's MediaCityUK studios used for filming Dragon's Den.
MediaCityUK is a large media development at Salford Quays in Greater Manchester. The BBC relocated major operations there from 2011, making the site a base for television, radio and digital production. Dragon's Den has been filmed at the BBC's Salford studios as part of that wider production presence.
Manchester is a common answer because MediaCityUK is in Greater Manchester and is closely associated with the region's media industry. Administratively, however, the development is in Salford, across the River Irwell from central Manchester.
The location also connects Dragon's Den with other BBC programmes produced in the north of England. The studio setting is different from the fictional or theatrical idea of a den: the pitches are recorded in a professional television production facility.