GCHQ
Government electronic surveillance agency. Now have huge mcr presence through direct and cover businesses. Main HQ in Heron House, Albert Square over the Slug and Lettuce which appears to be rented directly from the council
Interior views: https://www.tjmprojects.co.uk/projects/manchester-city-council/
https://www.gchq-careers.co.uk/transcripts/unique-solutions-to-unique-problems.html
https://mspl.co.uk/news/cisco-to-help-establish-gchq-engineer-accelerator-in-manchester/
https://mspl.co.uk/news/gchq-launches-first-manchester-tech-start-up-accelerator/
More recent job adverts refer to offices in “Manchester / Greater Manchester”, which we believe means they have multiple offices in the region. These may or may not be colocated with other organisations, we have no evidence either way yet