I tested my vit D levels in December 2013 and found that I was ‘insufficient’ and supplemented through the winter months with a high dose of Vit D and retested a year later and my levels were back in the ‘normal’ range.
The NHS Pathology Department at City Hospital Birmingham have a home test Vit D kit that you can purchase over the phone (this is how I tested my levels). Link http://www.vitamindtest.org.uk (Just to add as a caveat, I have not link with NHS City Hospital Trust and am only providing this link for information purposes)