The terahertz (THz) part of the electromagnetic spectrum lies between the domains of microwaves and optics. In the last 20 years there has been enormous growth in research on exploiting this spectral window for materials research and practical applications like security and medical screening. Many applications rely on sources of extremely short pulses of THz radiation and are limited by their presently low peak and average power. The recently discovered phenomenon of terahertz supercontinuum generation during the formation of laser ionized plasmas in free space combines remarkably broad, continuous and controllable bandwidth, stretching from the far to the mid infrared, with pulse energies as high as a micro-Joule. It promises to be an important new source of high peak and average power terahertz radiation for scientific studies of materials in extreme THz fields and for imaging and sensing. Its potential exploitation is however constrained by the low optical to THz conversion efficency, which is limited by diffraction, and the cost and low pulse repetition rate of the high energy laser systems currently needed. Our primary aim is to overcome these limitations by spatially confining the THz generation to the hollow core of a gas filled waveguide based on a type recently developed in Bath known as photonic crystal fiber. The combination of small core area and long interaction length is expected to reduce the threshold pump energy for THz generation by orders of magnitude. The optical waveguide will be integrated with a terahertz guide. By engineering the velocities of the optical and teraherts waves by composite waveguide design to achive a condition called 'phase matching' we will at the same time increase the conversion efficiency and thus retain the high peak power of the THz radiation. A secondary aim is to perform sensitive detection in similar composite guides by exploiting an intinsic optical nonlinearitiy of gases, thus creating the essential building blocks of what could be, with the addition of powerful fiber amplifiers currently in commercial development, a cost effective and robust 'all-fiber' platform for THz science and technology with unprecedented power and flexibility. This is our long term vision and ambition.