Hi Lupin, " franceunderpants " love the name anyway that is spot on, it is very low if its B12 your talking about.
Can you get Methylcobalamin in UK ?, if you can i would use 1 to 5 mg daily taking seperatly to a good quality multi B [ you need the multi B to help the b12 work better]
I take a Multi B in the morning and the B12 some other time of the day.
If you can't get Methylcobalamin, Cynocobalamin will also do the job but Methl is the prefered B12 as its the active form of b12, doesn't have to be converted by your liver like Cyno has to.
good luck
Brian