deep extragalactic infrared observations. As a result, as part of the *Spitzer* Wide-area Infrared Extragalactic survey (SWIRE; @2003PASP..115..897L) sensitive infrared observations of $\approx$ 14 deg$^2$ of the Lockman Hole area have been made. The availability of deep infrared observations in the Lockman Hole has triggered deep observing campaigns at optical, X-ray and radio wavelengths (e.g. ). The availability of data at such a wide range of frequencies makes the Lockman Hole a particularly good area for a multi-wavelength study of the faint radio source population.

In Paper I we selected a sample of 296 sources from the 10C sample in the Lockman Hole. By matching this catalogue to several lower frequency surveys we have investigated the radio properties of the sources in this sample; all but 30 of the 10C sources are matched to sources in one or more of these surveys. We found a significant increase in the proportion of flat-spectrum sources at flux densities below $\approx$1 mJy – the median spectral index between 15.7 GHz and 610 MHz changes from $\alpha =0.75$ for flux densities greater than 1.5 mJy to $\alpha =0.08$ for flux densities less than 0.8 mJy (the convention $S \propto \nu ^{-\alpha}$, for a source 