The results of an extremely deep, 8-d long observation of the central kpc of the nearby starburst galaxy M82 using Multi-Element Radio Linked Interferometer Network (MERLIN) at 5GHz are presented. The 17{mu}Jy/beam rms noise level in the naturally weighted image makes it the most sensitive high-resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as H ii regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7pc, with a mean size of 2.9pc.