Would this qualification give me the same job prospects as a TEFL Certificate (considering there is less global demand for French/Italian/Spanish than English)?
Yes. The market for French, Italian and Spanish is strong in both London and Europe. This qualification is also beneficial if you want to teach English in parallel with your native language, as the course covers the basic methodology used in all language learning.
Potential employers will check at interview stage whether you can transfer your teaching skills from one language to another. In London, studying a foreign language is important for business and as a hobby, so French, Italian and Spanish lessons are widely in demand.