BPSS clearance should be conducted during the pre-employment phase. It is a minimum requirement for those working in government, the armed forces, and for government contractors. The checks are often necessary before submitting an application for higher-level security clearance.

Pre-employment:  BPSS clearance is typically the first step in the background screening process for individuals who will have access to sensitive information or assets.

Before Security Clearance:  BPSS is a prerequisite for many higher-level security clearances, such as those required for access to Parliament or other sensitive government locations.

Ongoing Checks:  While primarily a pre-employment measure, ongoing checks may be necessary in certain situations to ensure continued compliance with security standards.

In essence, BPSS clearance is a foundational step to verify the identity, right to work, and trustworthiness of individuals before they are granted access to government or other sensitive environments.