The radiation tolerance testing of materials or optoelectronic components in a nuclear reactor requires a careful determination of the different components of the mixed gamma-neutron field. While the characterization of the neutron field can be performed using, for example, activation foils and validated by Monte-Carlo computation codes, the experimental measurement of the in-reactor gamma dose rate requires the use of costly ionization chambers. In this paper, we evaluate the possibility of using Red Perspex from Harwell Technologies for routine gamma dosimetry in mixed gamma neutron field. Self-powered gamma detectors and ionization chambers were used as reference dosimeters. We show that the accuracy of the Red 4034 dosimeters is better than 10% in mixed gamma-neutron fields.