5.21 The Treasury has also developed the Standardisation of PFI Contracts (SoPC), which sets out a standard approach to the risk allocation between the public and private sectors and includes principles and drafting for the key contractual clauses. The latest version, SoPC4, was released in March 2007 and is mandatory for all PFI contracts. In addition, each of the key sectors has in place a fully developed SoPC - compliant standard form contract. Any derogations from SoPC or the relevant standard form contract must be cleared by the Treasury.