We consider the simplest optimal control problem with one nonregular mixed constraint $G(x,u)\le0,$ i.e., such a that gradient $G_u(x, u)$ can vanish on surface $G = 0.$ Using Dubovitskii--Milyutin theorem approximate separation of convex cones, we prove first order necessary condition for weak minimum in form so-called local principle, which is formulated terms functions bounded variation, int...