There is no code of practice specifically regarding visits to ethnic restaurants. The UK Border Agency has, however, issued a code of practice for employers on how civil penalties for illegal working are issued and determined and this is available to view at: www.ukba.homeoffice.gov.uk/employers/preventingillegalworking/.
UK Border Agency staff are required to follow published guidance on how to conduct enforcement visits. Prior to a visit a thorough risk assessment is completed in conjunction with the police which includes an assessment of impact on the local community. The full guidance is available in chapter 31 of the enforcement guidance and can be viewed at: www.ukba.home office.gov.uk/sitecontent/documents/policyandlaw/enforcement/oemsectione/.