A technique based on specular reflection of polarised neutrons, complemented by polarisation analysis and small-angle (diffuse) scattering under reflection has been suggested for determination of parameters of domain structure of thin (∼ 10-10³ nm) films. The generalised matrix formalism developed to cope with the problem of reflection of neutrons from layered magnetic media with magnetisation arbitrary in magnitude and direction allowed to describe the specular reflection from unmagnetised films. It has been shown that under total reflection the local (averaged over the region coherently illuminated by a neutron) magnetic induction, the mean (averaged over the sample) magnetic induction and the mean square direction cosines of the magnetic induction enter into the reflection and depolarisation matrices. It has also been shown that the first two Fourier transform coefficients of the angular distribution function of the domain magnetisation, connected with the mean magnetisation and magnetic texture, can be experimentally found. The study of magnetisation processes in Fe₃₆Co₆₄ (170 ± 3 nm) and Co (110 ± 3 nm) films demonstrates the possibilities of the new technique. The optical effect of averaging over the region coherently illuminated by a neutron, effectively leading to a decrease in the 'local' measured magnetic induction of the Co film, has been observed for the first time.