Interserve will provide daily cleaning, window cleaning and periodic cleaning services to all of SSE and SGN's 70 corporate offices around the UK.
SGN is 50% owned by SSE. Interserve already provides asbestos removal services to both SSE and SGN industrial sites.
Promised innovations that helped Interserve secure the account include new management and timekeeping systems.
Managing director Jeff Flanagan said: “We look forward to starting a new partnership with SSE and SGN. Our experience of delivering consistent, cost-effective cleaning services for customers with large and diverse corporate estates makes us the perfect choice for this account, and we look forward to building on this relationship in the years to come.”
Meanwhile, there is still no news from Interserve of what plans it has for RMD Kwikform, its £200m-a-year formwork subsidiary. It announced a 'strategic review' of the business in February 2016, but eight months on it appears that a suitable buyer has yet to be found.