The NICE guidance on testing recognises that 20% of the elderly are B12 deficient and it is commoner in women. It raises the issues of adhering to equality legislation. In the presence of suggestive symptoms and a significant family history I believe that a failure to carry out MMA or active B12 testing could well breach the legislation provided of course that you are an elderly woman!
NICE recognises that these tests are more accurate diagnostic measures that could pick up cases earlier saving the NHS (and the patient!) from the consequences of an inadequate diagnosis and treatment.
Amazingly it then fails to recommend carrying out further diagnostic tests which appears contrary to its undoubtedly accurate observations.