Information derived from tomographic images has demonstrated the extreme variability of the ionosphere over the UK, with structures within the electron concentration usually associated with the auroral zone being found at UK latitudes under disturbed geomagnetic conditions. The tomographic images indicate that the main trough in the F-layer electron concentration is routinely present over the northern UK at nighttime. With an enhanced geomagnetic disturbance the progression of the trough to lower latitudes is evidenced, while extremely disturbed conditions result in the trough minimum being as far south as northern France. The applicability of the tomographic technique to the production of an ionospheric model, that includes the prominent main trough in the plasma electron concentration, has been demonstrated. Initial results indicate that the model shows potential for modelling an accurate representation of the main trough extending to some 30° in longitude from the location of the input data. Ray tracing through the resulting tomographic images and the model of the mid-latitude trough has direct applications for the near-real-time determination of radio propagation conditions.