Do the sums. Off peak is around half the price so yes off peak would be cheaper on those figures.
It is not as easy as that, I moved out of my parents house in the 70's at that time single glazed with coke fires, my memory of the house was on cool days fire lit at around 5 pm and only on cold days lit in the morning, and the only problem I remember was a cold house, never recall the house getting too hot.
Before my mother died we had to return to the house to look after her, now cavity wall insulation, double glazing, gas fired combi boiler condensating, and radiators and TRV's in every room, and it was realised the problem was the bay window, it was a sun trap, so in the morning the radiator would start heating the living room, then the sun came out, radiator already hot by this time so combination resulted in room hitting 28°C. What was needed was for the radiator TRV to act faster so it turned off the radiator faster when the sun came out, so electronic heads fitted to radiators which reduced the temperature when sun came out to 24°C. Still hotter than wanted but within acceptable limits.
The main problem was bay window and double glazing, but the point is that central heating was OK until house was made more thermal efficient. So a 1980's storage radiator system may have worked, but today when the sun hits the windows, the heating must be able to switch off, not just down.
OK it seems this flat only has one south facing window, so likely OK, but outbuildings, trees, hills all affect the heating plus direction of windows, and we don't tend to fit automatic louvre opener on a house today, only used in green houses, but in real terms the house can become a green house. It clearly depends on the home not all homes have same problem, and even the amount of flies, and security will determine if windows can be left open, on sunny days I will get up at 6 am and open the doors in house to allow house to cool as much as possible, then close again at 8 am to keep house cool, as it is too well insulated to cool down naturally over night.
Living style also changed heating requirements, away at work all day, and home at 6 pm you want a timer on heating, but with a varied return time you want geofencing. It is easy enough to fit either TRV or wall thermostat which can geofence, but most wall thermostats have a limit of around 5 amp some times lower, there are thermostats designed for under floor electric heating which can handle 16 amp, but under floor heating no good for geofencing it is again too slow to react, how much you want to spend is also a limiting factor.
It is all well and good saying what you want is fan assisted twin core radiators in every room to control the temperature nearly spot on and react fast, one core heats other core cools, it seems ideal, until you consider noise of fan running. So every heating system is a compromise, there is no perfect system, and government has not helped, OK good intentions with rules on zone heating, and energy ratings, even my caravan has plastic double glazed windows, and blown air central heating both gas and electric powered.
But I have lived in one house in Wales with gas blown air central heating, very expensive to run as house single glazed and it was blowing warm air past a cold window, and it also made the house very dry. Latter houses in the estate went to circulated water central heating. And if you put 4 thermometers in a room, you will see the room is not at one temperature, mothers house with that bay window the temperature could vary 10°C within the room.