I blame the countries physics teachers for so many questions similar to this being asked – and so many offering the wrong answer.
It is most economic to have the heating off at times that you are not in the house. This may require a sudden boost of energy when you return - but how do I know this will be less than that used to maintain the house temperature (or even a slightly reduced temperature), while you are out?
The simple answer is that with the heating off, the internal house temperature will cool, once cool (and even during cooling) the loss of heat energy (through the walls/ceiling) will slow due to a reduced thermal gradient (across the walls/ceiling) – eventually dropping to zero, when the room and outside temperature reach equilibrium. With the room temperature maintained at 18-20ºC, the thermal gradient will be much higher, with a constant (higher) heat energy loss.
I know people who have their immersion heater (used only for bath water) on 24/7. Believing it to be more efficient than turning it on only when they want a bath. Although I suppose one advantage is that they don’t have to wait an hour for the water to heat up.