The invention relates to a gas phase polymerisation process for the production of ethylene polymers in the presence of a catalyst composition based on a chromium compound, a titanium compound and a silica support material. The silica support material has a surface area (SA) between 685 m2/g and 800 m2/g, a pore volume (PV) between 1.65 and 1.85 cm3/g and an average particle size in the range between 25 and 35 micrometres. The catalyst composition is injected by a dry catalyst feeder into the polymerization reactor.