Axial torsion tests on pultruded glass fibre reinforced polymer (GFRP) composite circular cross-section tubes were carried out. The torque, angle of twist and surface strain were recorded during each test. The test data was used to plot linear graphs of shear stress versus shear strain, from which the the tubes’ mean in-plane shear modulus was determined. Thereafter, simply supported three-point flexure tests were carried out for a range of tube spans and axial orientations. The latter enabled any effects due to differences in tube wall thickness, arising from the pultrusion process, to be identified. From the load versus mid-span deflection data, the tubes’ elastic flexural moduli due to combined bending and shear and bending alone were quantified. It was shown, for span to diameter ratios ranging from 25:1 to 10:1, that the elastic modulus increased by 1.7 to 6.1% by taking account of the in-plane shear modulus