Developed Vetting (eDV), and STRAP. The BPSS is the entry-level National Security Clearance, and both CTC and EBS are effectively enhancements to the BPSS, with CTC relating to checking for susceptibility to extremist persuasion, and EBS relating to checking for susceptibility to espionage persuasion, the latter being needed for supervised access to SECRET material. The SC again is focused on susceptibility to espionage persuasion, and is required for an individual to have long-term unsupervised access to SECRET material and occasional access to TOP SECRET (TS) material, whilst for regular access to TS the DV, eDV is required. Occasionally STRAP is required with DV. Those with National Security Clearance are commonly required to sign a statement to the effect that they agree to abide by the restrictions of the Official Secrets Act (OSA). This is popularly referred to as "signing the Official Secrets Act". Signing this has no effect on which actions are legal, as the act is a law, not a contract, and individuals are bound by it whether or not they have signed it. Signing it is intended more as a reminder to the person that they are under such obligations. To this end, it is common to sign this statement both before and after a period of employment that involves access to secrets. National Security Clearance history After the United States entered into World War II, Britain changed its security classifications to match those of the U.S.. Previously, classifications had included the top classification "Most Secret", but it soon became apparent that the United States did not fully understand the UK's classifications, and classified information appeared in the U.S.'s press. This spearheaded the uniformity in classification between the United Kingdom and the United States. The terminology and levels of British security classifications have also changed from Positive Vetting and Enhanced Positive Vetting to SC, eSC, DV, eDV and STRAP. Other UK clearances In addition to National Security Clearances, other types of roles and organisations stipulate a need for clearances, including: Vulnerable Group Access (including children), as operated by the Disclosure and Barring Service (DBS), replacing former Criminal Records Bureau (CRB) and Independent Safeguarding Authority (ISA) checks Law Enforcement, with a hierarchy of Police Personnel Vetting (PPV) and Non-Police Personnel Vetting (NPPV) levels. United States In the United States, a security clearance is an official determination that an individual may access information classified by the United States Government. Security