20 There are also authorities to the effect that if the jurisdiction of the court is limited by statute, it cannot be enlarged by estoppel: Welch v Nagy [1950] 1 KB 455; J & F Stone Lighting & Radio Ltd v Levitt [1947] AC 209. However, caution is required when considering statements in the authorities about estoppel. For example, in J & F Stone Lighting, which was relied on in Welch v Nagy, the court was referring to issue estoppel (and res judicata). The doctrines of res judicata and issue estoppel do not apply to a decision of an inferior court made without jurisdiction because, unless the statute conferring jurisdiction otherwise provides, the decision is a nullity: Bower GS, Turner AK and Handley KR, The Doctrine of Res Judicata (3rd ed, 1996) [110] - [115]. The same is not true of a decision of a superior court of general jurisdiction. As Martin B said in Scott v Bennett (1871) LR 5 HL 234 at 245: