"We propose to construct and prototype an innovative high-precision time-of-flight system suitable for large areas, up to tens of square metres. The TORCH (Time Of internally Reflected CHerenkov light) detector provides a time-of-flight measurement from the imaging of photons emitted in a 1 cm thick quartz radiator, based on the Cherenkov principle. The photons propagate by total internal reflection to the edge of the quartz plane and are then focused onto an array of Micro-Channel Plate (MCP) photon detectors at the periphery of the detector. A timing resolution of 15 ps per particle can be achieved over a flight distance of 10 m. This will allow particle identification in the challenging intermediate momentum region, up to 20 GeV/c. The TORCH detector is highly compact, and the technique will have wide-ranging use in particle and nuclear physics experiments, and especially those where space is at a premium.The work involves a number of ground-breaking and challenging techniques. We will develop ultra-fast Micro-Channel Plate (MCP) photon detectors that can survive for several years in high radiation environments. The MCPs will be procured in industry to our specification with customized active area and granularity. We will also develop state-of-the-art electronics to read out the MCPs with picosecond precision. Photon imaging will be achieved with milliradian resolution over the large optical volume of the TORCH.Whilst the TORCH detector has its primary application in the field of particle physics, the MCP and optical developments will also have applications in space physics, nuclear physics, as well as medical imaging."