In 2021 the UK CCGT fleet achieved 49.9% efficiency (below design efficiency because of other factors we won't go into here).
I don't know where you get 49.9% from, sounds very high to me, and excerpt from Wiki below.
"The energy efficiency of a conventional thermal power station is defined as saleable energy produced as a percent of the
heating value of the fuel consumed. A simple cycle
gas turbine achieves energy conversion efficiencies from 20 to 35%.
[3] Typical coal-based power plants operating at steam pressures of 170 bar and 570 °C run at efficiency of 35 to 38%,
[4] with state-of-the-art fossil fuel plants at 46% efficiency.
[5] Combined-cycle systems can reach higher values. As with all heat engines, their efficiency is limited, and governed by the laws of
thermodynamics."
I don't know what state-of-the-art means in this context, but I wouldn't mind betting it doesn't apply to most electric generated in UK. Then there are transmission losses.
On the other hand, burning gas in a boiler at home with an, amazing really, efficiency of 90% means that for every unit of gas energy you use, you get 0.9 units of heat energy.
I believe modern boilers are more like 93% efficient (haven't looked up figures lately) but there's nothing amazing about it. Burning fuel in a boiler to produce heat is completely different from producing shaft power hence electricity. It's the 38% from the latter that's impressive!
And at first glance you seem to be comparing 2 units of energy into a power station with 1 into a boiler.
Taking generation efficiency 35% including transmission losses and COP 3, 1 unit of energy gives 0.35*3 = 1.05 from a heat pump, vs perhaps 0.93 from a boiler. Good for the planet if the electric is green, but with fossil fuel not much in it.