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-C20-alkyl, tri(C1-C20-alkyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl; each R2 is independently hydrogen or a C1-C20 hydrocarbyl radical provided that at least one R2 is not hydrogen; each R5 is independently hydrogen or a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16; each R6 is independently hydrogen or a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16; each n is independently 1, 2 or 3; and each R8 is a C1-20 hydrocarbyl group; and (ii) a cocatalyst comprising a compound of a group 13 metal, e.g. Al or boron.