Where is the best place to get vitamin d levels checked in the UK

The links provided in the vitamin D book in the forum , only recommend places to get vitamin d levels checked in the USA. Is there anywhere reliable in the UK (NHS?? perhaps this is a bit optimistic!!!)

Also what do I need to get checked ? is it just the 25(oh) d level, or anything else?

I am very interested in this as, my biggest respites from my CFS (POSITIVE FOR BORRELIA AND CPN) seems to happen when I holiday abroad. I love the sun and can sunbathe for hours . This may be because I am away from the stresses and strains of normal life, or both, but I have nearly always got worse during the winter.

Also when I get back from holiday , it only takes a few days when things start to go downhill once again