This paper highlights several key aspects of introducing series compensation (SC) in the UK transmission network and those requirements which would require the use of thyristor controlled series capacitors (TCSC) rather than the simpler fixed series capacitor (FSC) option. The paper then indicates how the main component values can be derived, provided that a clear functional specification is provided indicating the required level of compensation, steady state currents and overload currents. It also indicates a possible issue with regard to the number of times that the capacitor can remain in service under severe storm conditions with successful auto recloses which may require exceedingly large MO Vs. (5 pages)