This paper presents the key findings of an ESA-funded programme of work to investigate refractive systems and their application to precision polarimetry experiments. We briefly summarize the derivation of requirements on the optical system for CMB polarimetry, and the design of a refractive telescope system which meets these stringent requirements. An extensive programme of experimental work was undertaken in order to better understand the optical, thermal and mechanical characteristics of the lens material, and of lenses made from this material. A repeatable and controllable antireflection coating procedure was developed and validated, and used to coat lenses used in this study. Optical measurements before and after coating have been used to validate a new module for an industry-standard antenna modelling software package.