Norah, as many have said, no, nowadays, having it on all the time uses up more fuel than having it on twice a day in a reasonably insulated house.
I undertstand the maths of it, and could illustrate it with a graph, but trying to explain it is less easy. Essentally it is a function of how much heat is lost during the hours the heating is not on, against how much fuel is used to return it to the chosen temperature.
If you have 20 degrees set on the thermostat and a house with no insulation at all and no heating on between, say, 9.00am and 4.00pm, then on a freezing day like today the temperature could fall to 10 degrees or less, which, discomfort apart, would take a heck of lot fuel to get it back to 20. Probably more than if the heating stayed at a high level and just kept coming on and off all day.
However if you lived in a modern well insulated house, with the heating coming on twice a day to the same pattern the heating might only fall to 18 degrees and the amount of fuel needed to get the house back up to 20 degrees will be less than of you had the heating all day constant;y coming on and off to keep the temperature at 20 degrees