A catalyst in solid particulate form free from an external carrier material comprising (i) a 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, C1-20-alkyl, tri(C1-20-alkyl)silyl, C6-20-aryl, C7-20-arylalkyl or C7-20-alkylaryl; R2 is a C1-20-hydrocarbyl radical; R2′ is a C1-20-hydrocarbyl radical; R6 is a linear or branched aliphatic C1-20-hydrocarbyl group, SR9 or OR9; R6′ is a linear or branched aliphatic C1-20-hydrocarbyl group, SR9′ or OR9′; with the proviso that neither R6 or R6′ represents a group having a quaternary carbon atom directly attached to the indenyl ring; R9 is a C1-20-hydrocarbyl group; R9′ is a C1-20-hydrocarbyl group; Ar is a C6-12-aryl or C5-12-heteroaryl group optionally carrying one or more substituents R8; Ar′ is a C6-12-aryl or C5-12-heteroaryl group optionally carrying one or more substituents R8′; each R8 is a C1-20-hydrocarbyl group; each R8′ is a C1-20-hydrocarbyl group; and wherein at least two of R2 and R2′; R6 and R6′; or Ar and Ar′ are the same; and (ii) a cocatalyst comprising a compound of a group 13 metal, e.g. Al or boron.