During the first 24 months of the I.FAST project, a novel electro-optic waveguide sensor has been developed that is suitable for high-bandwidth beam position measurements of the electric field of a passing relativistic particle bunch. Following optimisation of the electromagnetic design, a pair of such waveguide sensors were manufactured and incorporated into a prototype Electro-Optic Beam Position Monitor at Royal Holloway University of London. The prototype was first bench tested and then shipped to CERN for a series of beam tests at CERN’s HiRadMat and CLEAR facilities, to assess the signal sensitivity and time response respectively. The results of the beam test campaign are documented here.