Take a ruler or tape measure up into your roof space. You can usually do this safely standing on a ladder and peering into the ceiling hatch.
Insulation that doesn't meet HomeFit standard – this shows less than 120mm thick (or R2.2). This can be confirmed by an assessor, by installers receipt or by label stapled in the ceiling. To be HomeFit® Plus standard, insulation would need to be R3.2 (R3.6 in Zone 3). Higher levels of insulation are recognised with additional points.