London's commercial cleaning buyers range from a ten-person agency in a Shoreditch warehouse to a managed office building in the City with a facilities team and a formal tender.
Many buildings are cleaned before 7am or after 6pm to avoid disruption, so staffing and supervision are the real product.
Buyers ask about accreditation early: CHAS or SafeContractor for health and safety, ISO standards for larger contracts, BICSc training, and whether you pay the London Living Wage (a voluntary pay rate set above the legal minimum), which some public bodies and larger employers ask for.
There is no licence to clean, so this proof does the job a licence would. Travel matters too, because cleaning staff rely on public transport and night buses.