I would take 400ug a day of folic acid and an iron supplement. You don't need a lot of iron. I take Solgar Gentle Iron as it's easily absorbed and doesn't cause me any intestinal problems.
I don't know Berocca, no idea if it's good. I would personally leave out the spray and just go with sublinguals (or even just injections as that should already be more than enough), injections, good iron and good B-complex. See how that goes for a couple of weeks.
If you like the fizz of Berocca (a multi-B supplement with up to 900% RDA of some vitamins) then it should be OK (only 7.1 mg of B6 - which is the one to watch out for).
However, you're probably paying a lot of money for highly nutritious urine. Being water soluble the B vitamins will be excreted in the urine (you may notice your pee is a nice bright yellow - thanks to all that expensive B12 going into the pan).
I'd recommend trying Tesco multi-B Vitamins - 100% of the RDA of all B vits for just 2p a tablet (about 5% the cost of Berocca)
Page 29 from BCSH Cobalamin and Folate guidelines is a diagnosis flowchart that shows the process a medic should follow with someone they suspect may have B12 deficiency. Page 8 in same document gives details of UK B12 treatment.
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