You're possibly thinking of an Open Cycle gas turbine, where we burn gas, it spins the turbine, and the hot exhaust is lost energy. The UK has a negligible amount of this in electricity production and obviously with higher fuel prices there's ever less reason to use that small capacity. The 30GW or so gas turbine electricity in the UK is Combined Cycle, so the exhaust heat runs a secondary steam turbine bringing them up past 50% efficiency.