One way of resolving the conflict between DA Reg 7(2)(i) / 8(14) and HB(SPC) Reg 60 could be found in the doctrine of implied repeal. This doctrine basically states that Parliament may not bind itself in terms of future legislation, therefore an earlier statute cannot restrict the appliation of a later statute. Where two statutes of equal status (e.g. two acts of parliament, or two statutory instruments) contain inconsistent provisions, the later provision is assumed to have impliedly repealed the part of the earlier statute with which it is inconsistent.
So I guess whichever came latest is the one to follow, in this case it would be the HB(SPC) Regs since they came into force in 2006 whereas the DA Regs came into force in 2001.
So where Pension credit has been awarded and it is an advantageous change, it would take effect from the following Monday – if you agree with my argument that is!!!