Active galaxies are the most powerful engines in the Universe for converting gravitational energy into radiation, and their study at all epochs of evolution is therefore important. Powerful radio-loud quasars and radio galaxies have the added advantage that, since their radio jets need X-ray-emitting gas as a medium in which to propagate, the sources can be used as cosmological probes to trace significant atmospheres at high redshift. The radio emission can be used as a measure of source orientation, and sensitive X-ray measurements, especially when used in combination with multi-wavelength data, can be used to derive important results on the physical structures on a range of sizes from the cores to the large-scale components. In this paper we present new results on a significant sample of powerful radio galaxies and quasars at z > 0.5, drawn from the 3CRR catalogue and selected to sample a full range of source orientation. Using high-quality observations from XMM-Newton and Chandra, we discuss the X-ray properties of the cores, jets, lobes and cluster gas, and, through the incorporation of multiwavelength data, draw conclusions about the nature of the emission from the different components.