In recent history, the British electricity sector landscape has changed as more renewables, particularly solar and wind, are connected to the power system. Since 2004, electricity generated from renewables in the UK has increased tenfold, and in 2019 37.1% of total electricity generated was from renewable sources. These changes have far-reaching implications for the operation of national electricity networks and for ensuring security of supply. Current and emerging system operability concerns in GB cover a broad range of topics. Work recently completed at the University of Strathclyde, outlined in this report, has reviewed: how the British Electricity System Operator, National Grid ESO (NGESO) currently uses balancing services to manage the power system; possibilities for the future provision of frequency response and reserve; prospects for short circuit current support from power electronic converters; and market changes required to avoid the need for NGESO to constrain on fossil-fuelled generation to support system operability in 2025.