Complex sentence: The firm's offices were located in Portland Place London close to the RIBA and it employed 56 associates and assistants over the years, many of whom went on to set up their own practices (for example James Stirling and James Gowan).
Split into simpler sentences: The firm's offices were located in Portland Place London close to the RIBA. They employed 56 associates and assistants over the years, many of whom went on to set up their own practices (for example James Stirling and James Gowan).