TORCH is a novel time-of-flight detector, designed to provide $\pi$/K particle identification up to 10$\,\text{GeV}/c$ momentum over a 10$\,$m flight path. Based on the DIRC principle, Cherenkov photons are produced in a quartz plate of 10$\,$mm thickness, where they propagate to the periphery of the plate by total-internal reflection. There the photons are focused onto an array of micro-channel plate photomultipliers (MCP-PMTs) which measure their arrival times and spatial positions. A time resolution of 70 ps per detected Cherenkov photon is expected, which results in a time-of-flight resolution of 15 ps, given typically 30 detected photons per track. For a future application, a full-scale TORCH detector has been proposed for the future LHCb upgrade, which comprises 18 modules with 198 MCP-PMTs. To demonstrate the TORCH principle, a half-height ($1250\times660\times10 \,\text{mm}^3$) prototype module has been tested in a 8$\,\text{GeV}/c$ mixed proton-pion beam at the CERN PS. Customised $53\times53\,\text{mm}^2$ MCP-PMTs of effective granularity $128\times8$ pixels have been employed, which have been developed in collaboration with an industrial partner. The single-photon timing performance and photon yields have been measured and are close to specification, demonstrating the TORCH concept.