  We discuss how the combined analysis of $B\to K\nu\bar\nu$ and $B\to Kl^+l^-$
can provide us with new physics tests practically free of form factor
uncertainties. Residual theory errors are at the level of several percent. This
study underlines the excellent motivation for measuring these modes at a Super
Flavour Factory, or, in the case of $B\to Kl^+l^-$, also at a hadron collider.
