This paper generalises the Small Gain Theorem SGT to cope with switched linear systems. A switching strategy able to guarantee stability of the feedback interconnection of a switching linear subsystem and a linear stable norm-bounded perturbation is developed. The new version of SGT is specially important to solve two different problems. The first one concerns the possibility of enhancing the robustness of a feedback control system by appropriately orchestrating the switches among a set of given linear regulators. The second problem is the design of a stabilising switching strategy for time-delay switched systems. Both cases of state and output feedback switching laws are considered. Remarkably, since the sufficient conditions for the existence of a solution are delay-dependent, they are less conservative with respect to previous results in the literature. The theory is illustrated by means of academic examples.