Metathesis polymerisation can be effected with many catalysts under a variety of conditions. The system described here, viz., W(CO)6/CBr4/hv, induces polymerisation by in situ generation of the active species and has not been reported in the literature so far. In this paper, optimisation studies of this system, yields obtained with various monomers and characterisation of the active species are discussed. Variation of different parameters such as the ratio of W(CO)6:CBr4, the time of photolysis and the effect of solvents as well as that of the metal carbonyls have been studied. In addition, copolymers of phenylacetylene and norbomene have been synthesised. We have also attempted to characterise the active species responsible for the polymerisation by reaction with acetophenone.