A continuous anionic polymerisation or copolymerisation process of styrene or diene monomers with alkali metal alkyl as polymerisation initiator is carried out in the presence of a metal alkyl or aryl of an at least bivalent element as reaction speed regulator, preferably in non-isotherm conditions and without a back admixture in a pipe or pipe bundle reactor. A metal alkyl or aryl A of formula R1M1 and a metal alkyl or aryl B of formula R2nM2 in a molar ratio between B and A from 0.1:1 to 500:1 are used. In the formulas, M1 is Li, Na or K; R1 is hydrogen, C¿1?-C20-alkyl or C6-C20-aryl or C7-C20-alkyl-substituted aryl; M?2¿ is an n-valent element of groups 2a, 2b or 3a of the periodic table of elements; and R2 is hydrogen, halogen, C¿1?-C20-alkyl or C6-C20-alkyl. Also disclosed is a special initiator for the anionic polymerisation which does not contain any Lewis bases.