A process for the preparation of a heterophasic copolymer of propylene and ethylene comprising polymerizing 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-alkyl, tri(C1-C20-alkyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl; R2 is a C1-C20 hydrocarbyl radical; R5 is a C1-C20 hydrocarbyl radical; R6 is a tertiary C4-C20 hydrocarbyl radical; R7 is a hydrogen atom or a C1-10-hydrocarbyl radical; n is 0 to 3; R1 is a C1-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 of a Group 13 metal; wherein the xylene soluble fraction (XS) of the heterophasic copolymer of propylene and ethylene has an intrinsic viscosity of at least 1.5 dl/g and an ethylene content of 10 to 70 wt %.