A process for producing copolymers of ethylene and at least one alpha-olefin having from 4 to 10 carbon atoms in the presence of a polymerisation catalyst which is a solid Ziegler-Natta catalyst component for ethylene polymerisation, and a cocatalyst, the copolymer having a density of from 906 to 937 kg/m 3 and a melt flow rate MFR 21 measured at 190 °C under 21.6 kg load of from 3 to 100 g/10 min comprising the steps of homopolymerising ethylene or copolymerising ethylene and a first alpha-olefin having from 4 to 10 carbon atoms in a first polymerisation stage in the presence of the polymerisation catalyst, hydrogen and optionally the first alpha-olefin wherein the molar ratio of hydrogen to ethylene in the fluid reaction mixture of the first polymerisation stage is from 200 to 50000 mol/kmol and the molar ratio of the first alpha-olefin to ethylene in the fluid reaction mixture of the first polymerisation stage is from 0 to 1500 mol/kmol, to produce a first homo- or copolymer of ethylene; introducing particles of the first homo- or copolymer of ethylene, containing active catalyst dispersed therein, together with additional ethylene, hydrogen and a second alpha-olefin having from 4 to 10 carbon atoms into a second polymerization stage and copolymerising ethylene and said second alpha-olefin having from 4 to 10 carbon atoms in said second polymerisation stage in the presence of the first homo- or copolymer of ethylene to produce a polymer mixture comprising the first homo- or copolymer of ethylene and a second copolymer of ethylene, the polymer mixture having a density of from 906 to 937 kg/m 3 and a melt flow rate MFR 21 of from 3 to 150 g/10 min; recovering the polymer mixture, characterised in that the solid Ziegler-Natta catalyst component comprises magnesium, titanium, halogen and an internal organic compound having the formula: wherein in the formula R 1 to R 5 are the same or different and can be hydrogen, a linear or branched C 1 to C 8 -alkyl group, or a C 3 -C 8 -alkylene group, or two or more of R 1 to R 5 can form a ring, and the two oxygen-containing rings are individually saturated or partially unsaturated or unsaturated. homopolymerising ethylene or copolymerising ethylene and a first alpha-olefin having from 4 to 10 carbon atoms in a first polymerisation stage in the presence of the polymerisation catalyst, hydrogen and optionally the first alpha-olefin wherein the molar ratio of hydrogen to ethylene in the fluid reaction mixture of the first polymerisation stage is from 200 to 50000 mol/kmol and the molar ratio of the first alpha-olefin to ethylene in the fluid reaction mixture of the first polymerisation stage is from 0 to 1500 mol/kmol, to produce a first homo- or copolymer of ethylene; introducing particles of the first homo- or copolymer of ethylene, containing active catalyst dispersed therein, together with additional ethylene, hydrogen and a second alpha-olefin having from 4 to 10 carbon atoms into a second polymerization stage and copolymerising ethylene and said second alpha-olefin having from 4 to 10 carbon atoms in said second polymerisation stage in the presence of the first homo- or copolymer of ethylene to produce a polymer mixture comprising the first homo- or copolymer of ethylene and a second copolymer of ethylene, the polymer mixture having a density of from 906 to 937 kg/m 3 and a melt flow rate MFR 21 of from 3 to 150 g/10 min; recovering the polymer mixture, characterised in that the solid Ziegler-Natta catalyst component comprises magnesium, titanium, halogen and an internal organic compound having the formula: wherein in the formula R 1 to R 5 are the same or different and can be hydrogen, a linear or branched C 1 to C 8 -alkyl group, or a C 3 -C 8 -alkylene group, or two or more of R 1 to R 5 can form a ring, and the two oxygen-containing rings are individually saturated or partially unsaturated or unsaturated.