I went to a naturopath for a while. She gave me emails to show my GP so he knew what blood tests she would like done. One showed up a deficiency in B12. The doctor hadn't thought of this and didn't offer me a supplement to put this right. He didn't even remark on the results of the tests
Hi zand, every UK diabetic gets or should get at least one blood test a year usually it tests for HbA1c and several other tests as well which will include red blood cells, platelets etc and it is these which will indicate to a doctor whether or not you may be anaemic and or have a B12 deficiency, because of this there is no need to have any further tests done as if you are B12 deficient you will have a low red blood cell count, if that is the case it is your doctor who should investigate why.
I asked my doctor whether I may be deficient once, he took a quick look at my lat bloods and said "no, your red blood cell count is better than mine" so there was nothing to worry about.
Long term use of metformin can in certain cases lead to a B12 deficiency, I dont know the time frames involved but it would imagine long term to mean years rather than months and as I have explained it will show up on your/our annual/bi annual/4 monthly blood test.
From BMJ research "Long term treatment with metformin in patients with T2 diabetes and risk of vitaimin b-12 deficiency: Randonised placebo controlled trial.
"Conclusions Long term treatment with metformin increases the risk of vitamin B-12 deficiency, which results in raised homocysteine concentrations. Vitamin B-12 deficiency is preventable; therefore, our findings suggest that regular measurement of vitamin B-12 concentrations during long term metformin treatment should be strongly considered."
http://www.bmj.com/content/340/bmj.c2181
So basically every doctor should check your red blood cell count at every blood test and take steps to investigate should you be at all anaemic.
Personally I would tent to put my trust in my doctor rather than a "naturapath" whatever that might be.
More information on B12 deficiency here.
http://www.patient.co.uk/health/vitamin-b12-deficiency-and-pernicious-anaemia