A process for the preparation of a propylene polymer in a multistage polymerisation process in the presence of a single site catalyst, said process comprising: (I) in a prepolymerisation step prepolymerising a single site catalyst in the presence of propylene and optionally at least one C2-10 alpha olefin comonomer and in the presence of hydrogen or in the absence of hydrogen; (II) in a slurry polymerisation step, polymerising propylene and optionally at least one C2-10 alpha olefin comonomer, with the pre-polymerised catalyst of step (I) in the presence of hydrogen; and subsequently (III) in a gas polymerisation step polymerising propylene and optionally at least one C2-10 alpha olefin comonomer, in the presence of catalyst and polymer from step (II) and optionally in the presence of hydrogen so as to form a propylene homopolymer or copolymer; wherein the amount of hydrogen fed to the pre-polymerisation step (I) is at most 15% of the total amount of hydrogen fed to steps (I) and (II) of the polymerisation process.