The inclusive branching ratio for the process b → τ−ν¯τ X has been measured using hadronic Z decays collected by the OPAL experiment at LEP in the years 1992–2000. The result is: BR(b → τ−ν¯τ X) = (2.78 ± 0.18 ± 0.51)%. This measurement is consistent with the Standard Model expectation and puts a constraint of tan β/M± H < 0.53 GeV−1 at the 95% confidence level on Type II Two Higgs Doublet Models.