A Unilateral Declaration of Independence (UDI) was issued in 1965 by the lawfully constituted government of Ian Smith and purported to establish the new sovereign state of Rhodesia.

However, in common with other states, the United Kingdom considered the UDI to be illegal and its parliament passed the Southern Rhodesia Act 1965 to permit the colonial governor to dismiss Smith's government.

Madzimbamuto's wife, Stella, challenged the legality of her husband's detention on the ground that the prolongation of the state of emergency was unlawful.

Rhodesia's Minister of Justice, Desmond Lardner-Burke, who had made the Order for Madzimbamuto's continuing detention, was named as Respondent.

The Appellate Division (Beadle CJ, Quenet JP, Macdonald JA; Fieldsend AJA, dissenting) ruled that a fresh detention order had to be made in order for Madzimbamuto's detention to continue under the 1966 regulations, but found that the Smith government was the de facto government of Rhodesia by virtue of its "effective control over the state's territory", and could "lawfully do anything which its predecessor could lawfully have done".

Sovereignty over Southern Rhodesia rested with the Crown of the United Kingdom and had not been affected by the unilateral declaration of independence.

Lord Reid rejected arguments that parliamentary sovereignty in the United Kingdom could be limited by constitutional conventions.

In obiter dictum, he also questioned whether the constitutional convention concerning Rhodesia's self-government continued to apply, in light of the Rhodesian government's rejection of British sovereignty through the UDI: It is often said that it would be unconstitutional for the United Kingdom Parliament to do certain things, meaning that the moral, political and other reasons against doing them are so strong that most people would regard it as highly improper if Parliament did these things.

They are only concerned with the legal powers of Parliament.Lord Pearce gave a dissenting judgment, in which he concluded that the detention orders should be upheld under the doctrine of necessity.