It has been reaffirmed that where part of a law is invalid for being beyond the powers of the lawmaker (ultra vires) the good in the law will not be separated from the bad if it is complicated and impractical to do so. If there is an incoherent remainder, the entire law will be set aside.
In a matter before the Supreme Court of Appeal it was found that the Minister of Mineral Resources had no power to pass regulations under the Mineral and Petroleum Resources Development Act 2002 regarding environmental matters because this was reserved for regulation under the National Environmental Management Act 1998 by the Minister of Environmental Affairs. The majority of the provisions of the petroleum regulations were therefore invalid because they were ultra vires.
The court refused to separate the invalid provisions from those that were authorised because it was not practical to do so. In addition, what would be left behind was not sufficiently coherent to survive on its own.
The same principle applies in relation to a contract which is partly invalid. There is a common boilerplate clause in contracts purporting to sever the invalid from the valid and thus to keep the contract alive. This is only possible if it can readily be done and if what is left is a coherent enforceable contract fulfilling the purposes of the contract as a whole.
The case is Minister of Mineral Resources v Stern & others.