[en] Inclusive inelastic electron scattering off the deuteron under 180 deg. has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm^-1 and 0.74 fm^-1 with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn→dγ of big-bang nucleosynthesis over most of the relevant temperature region. Results from potential model calculations and (for q=0.27 fm^-1) from pionless nuclear effective field theory are in excellent agreement with the data