The present invention relates to herbicidal benzyloxy-substituted phenyl-diones and benzyloxy substituted phenyl-dioxo-thiazinone derivatives of formula (I), as well as to processes and intermediates used for the preparation of such derivatives. The invention further extends to herbicidal compositions comprising such derivatives, as well as to the use of such compounds and compositions in controlling undesirable plant growth: in particular the use in controlling weeds, such as broad-leaved dicotyledonous weeds, in crops of useful plants.