Submillimetre Galaxies (SMGs) are high-redshift starbursts that are believed to be the precursors to modern-day giant elliptical galaxies. AGN appear to be an integral part of the evolution of these massive, star-forming galaxies; this is implied by the discovery of black holes at the centres of all nearby, massive galaxies and tracers of AGN activity have indeed been detected in a significant fraction of SMGs e.g. via deep X-ray observations and NIR spectroscopy, altough they appear not to be bolometrically dominant. Radio observations offer an alternative, dust-unobscured, route to quantifying the contribution of AGN to the SMG luminosity, but only if the starburst contribution can be removed. The most effective way of doing this is with high-resolution VLBI which filters out the low-brightness extended emission typical of star forming regions leaving only the compact AGN cores. We have observed three SMGs in the Lockman Hole using the European VLBI Network at a wavelength of 18~cm. All three are relatively bright (~250\,$\mu$Jy) and from MERLIN imaging were known to contain compact structure. Two of them are detected thus indicating that AGN are common in radio-detected SMGs and contribute significantly to the radio luminosity.