A catalyst in solid particulate form free from an external carrier material comprising (i) a complex of formula wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R' 2 C-, -R' 2 C-CR' 2 -, -R' 2 Si-, -R' 2 Si-SiR' 2 -,-R' 2 Ge-, wherein each R' is independently a hydrogen atom, C 1-20 -alkyl, tri(C 1-20 -alkyl)silyl, C 6-20 -aryl, C 7-20 -arylalkyl or C 7-20 -alkylaryl; R 2 is a C 1-20 -hydrocarbyl radical; R 2' is a C 1-20 -hydrocarbyl radical; R 6 is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9 or OR 9; R 6' is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9, or OR 9'; with the proviso that neither R 6 or R 6' represents a group having a quaternary carbon atom directly attached to the indenyl ring; R 9 is a C 1-20 -hydrocarbyl group; R 9' is a C 1-20 -hydrocarbyl group; Ar is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8; Ar' is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8'; each R 8 is a C 1-20 -hydrocarbyl group; each R 8, is a C 1-20 -hydrocarbyl group; wherein at least two of R 2 and R 2'; R 6 and R 6'; or Ar and Ar' are the same; and (ii) a cocatalyst comprising a compound of a group 13 metal, e.g. Al or boron. (i) a complex of formula wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R' 2 C-, -R' 2 C-CR' 2 -, -R' 2 Si-, -R' 2 Si-SiR' 2 -,-R' 2 Ge-, wherein each R' is independently a hydrogen atom, C 1-20 -alkyl, tri(C 1-20 -alkyl)silyl, C 6-20 -aryl, C 7-20 -arylalkyl or C 7-20 -alkylaryl; R 2 is a C 1-20 -hydrocarbyl radical; R 2' is a C 1-20 -hydrocarbyl radical; R 6 is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9 or OR 9; R 6' is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9, or OR 9'; with the proviso that neither R 6 or R 6' represents a group having a quaternary carbon atom directly attached to the indenyl ring; R 9 is a C 1-20 -hydrocarbyl group; R 9' is a C 1-20 -hydrocarbyl group; Ar is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8; Ar' is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8'; each R 8 is a C 1-20 -hydrocarbyl group; each R 8, is a C 1-20 -hydrocarbyl group; wherein at least two of R 2 and R 2'; R 6 and R 6'; or Ar and Ar' are the same; M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R' 2 C-, -R' 2 C-CR' 2 -, -R' 2 Si-, -R' 2 Si-SiR' 2 -,-R' 2 Ge-, wherein each R' is independently a hydrogen atom, C 1-20 -alkyl, tri(C 1-20 -alkyl)silyl, C 6-20 -aryl, C 7-20 -arylalkyl or C 7-20 -alkylaryl; R 2 is a C 1-20 -hydrocarbyl radical; R 2' is a C 1-20 -hydrocarbyl radical; R 6 is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9 or OR 9; R 6' is a linear or branched aliphatic C 1-20 -hydrocarbyl group, SR 9, or OR 9'; with the proviso that neither R 6 or R 6' represents a group having a quaternary carbon atom directly attached to the indenyl ring; R 9 is a C 1-20 -hydrocarbyl group; R 9' is a C 1-20 -hydrocarbyl group; Ar is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8; Ar' is a C 6-12 -aryl or C 5-12 -heteroaryl group optionally carrying one or more substituents R 8'; each R 8 is a C 1-20 -hydrocarbyl group; each R 8, is a C 1-20 -hydrocarbyl group; wherein at least two of R 2 and R 2'; R 6 and R 6'; or Ar and Ar' are the same; and (ii) a cocatalyst comprising a compound of a group 13 metal, e.g. Al or boron.