True, system thermal efficiency for the UK's CCGT generation is about 50%. Obviously that's with a varying throttle (the UK goes from say 5GW of CCGT to 25GW of CCGT in an hour if the wind drops just as everybody wakes up) and you'd do better than 50% if you were baseload running 24/7 at peak performance - but that's not a realistic place for CCGT to be when nuclear fuel is basically free and the two new big sources (solar and wind) aren't even running on actual fuel anyway.