In Sweden, with its long cold dark winters vitamin D tests are done routinely with your lipid panel.
Aotearoa, very rare to have vitamin D deficiency - much more likely to have too much dangerous sun exposure that damages your skin. So, not routine test.
I didn't think England/British isles was usually a sunny place, but big changes happening to the climate these days, huh?! Do you know what deficiency rates are in your place in the world? (Maybe traditionally there have been plenty of folks out in the sun gardening and tilling the soil, and the Health powers that be haven't kept up with the greater-indoors times? just suggesting...)
When I have gotten huge insulin resistance, vitamin D/sun deficiency has been a major contributing factor.
Vitamin D/the sun is a crucial part of a healthy blood glucose regulation system.