Data in several observables related to the decay b → c τ ν deviate from their Standard-Model
predictions. I discuss possible explanations in terms of new physics such as charged-Higgs boson
or leptoquark exchange. Then I present a phenomenological analysis using different B→ D^* form factor
calculations and advertise the recently measured D^* polarisation fraction in B→ D l nu, l=e,μ, decays
as an excellent discriminator between different form factor calculations.