If you answer yes to all or the majority of these questions it would be beneficial for you to consider

upgrading your insulation:

Ceiling level

Do you find the house loses heat quickly once the heating is turned off?

If the insulation in your attic is made from wool (fibreglass, sheeps wool, rock wool etc), is it less then 300mm thick?

Are the joists visible?

Is the insulation layer patchy, i.e.does thickness vary across the attic?

Is 50% or more of the attic floored, i.e. sheets of wooden flooring applied to the joists with wool insulation restricted to the depth of the joists below the flooring?

Rafter-level insulation

Do you find the house loses heat quickly once the heating is turned off?

If the insulation in your attic is made from wool (fibreglass, sheepswool, rock wool etc), is it less then 200mm thick?

Is the insulation made from another material and less than 150mm thick?