The spin states of W bosons in e+e- -> W+W- -> qqln events recorded by the OPAL detector at LEP are determined by an analysis of the angular distributions of their decay products. This information is used to calculate polarised differential cross-sections and to search for CP violating effects. Results are presented for W bosons produced in e+e- collisions with centre-of-mass energies between 183 GeV and 209 GeV. The average fraction of longitudinally polarised W bosons measured from the data is found to be consistent with the Standard Model prediction.