The original Dragon's Den studio was based in London before filming moved to Manchester.
The British programme was initially filmed in London, where the early series established the den's familiar industrial-looking set and presentation style. Production later moved north to Manchester, reflecting a broader use of regional production facilities by major broadcasters.
The city named in the answer refers to the original studio base, not the location of every entrepreneur or business featured in the programme. Pitches come from founders across the United Kingdom and can concern companies operating anywhere.
Manchester is therefore an important later production location, but it is not the answer to the question about the original studio. This distinction can cause confusion because many long-running viewers associate the current visual identity with the later Manchester period.