Here is a selection of sites which you may find of interest.

Elite Contact Security Ltd Trading as ECS Security holds SIA Approved Status for the provision of Security Guarding and Keyholding Services. CCAS is the assessing body.

The ACS Standard encompasses all aspects of a security provides operation.  It takes a histolic view of how well an organisation is managed and an approved organisation must demonstrate to an independent assessor, on an annual basis, that it has met defined standards.

SIA Registration Number 3516.  
http://www.sia.homeoffice.gov.uk/pages/acs-roac-intro.aspx