A process for the preparation of a copolymer of propylene and ethylene comprising polymerising propylene and ethylene in the gas phase in the presence of a solid particulate catalyst free from an external carrier comprising: (i) a symmetrical complex of formula (I), wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-SiR'2-, -R'2Ge-, wherein each R' is independently a hydrogen atom, C1-C20-alkyi, tri(C1- C20-aikyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl; R2 is a C1-C20 hydrocarbyl radical; m is 2 to 5; R9 is a H or C1-C20 hydrocarbyl radical; R7 is a hydrogen atom or a C1-10-hydrocarbyl radical; n is 0 to 3; R1 is a C 1-C20 hydrocarbyl radical and optionally two adjacent R1 groups taken together can form a further mono or multicyclic ring condensed to Ph ring optionally substituted by one or two groups R4; and R4 is a C1-C10 alkyl radical; and (ii) a cocatalyst, preferably comprising an organometallic compound
