In terms of the transitional provisions with respect to the H and C decision-making process, it comes into force on royal assent. Then there are certain exceptional transitional provisions that affect the timing for particular persons, depending on whether the claim is determined between royal assent and the coming into force of the RAD provisions, and retaining an ongoing opportunity for persons whose claims are pending after the coming into force of the appeal division provisions for a concurrent application for humanitarian and compassionate grounds.
On June 1st, 2010. See this statement in context.