A process for the preparation of a supported catalyst is disclosed, comprising the steps of a) contacting a support material containing 1-10% water with a trialkylaluminium compound; and b) contacting the resulting material with a complex of the formula (I) 1 wherein M is FenullIInull, FenullIIInull, ConullInull, ConullIInull, ConullIIInull, MnnullInull, MnnullIInull, MnnullIIInull, MnnullIVnull, RunullIInull, RunullIIInull or RunullIVnull; X represents an atom or group covalently or ionically bonded to the transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; R1 to R7 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiRnull3 where each Rnull is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl.