High-resolution streak photography has been used to show that, in laser-produced breakdown of helium in the initial pressure range 1 to 4 atm, the scattering of incident light at the breakdown front is due to reflection at the refractive index change in the quasi-spherical plasma boundary. The strongly non-linear variation of scattered intensity with initial gas pressure and the spatial distribution of the scattered laser light are explicable in terms of this mechanism. Interpretation of diagnostic data obtained from the scattered light in the study of radiation-driven breakdown waves is made more reliable if the scattering mechanism is known.