National guidelines are to move people with pernicious aneamia from the injection to something else, 50mcg isn't enough, 1000 - 2000mcg tablets/sub linguals etc are recommended, 1 a day. It isn't a Brexit thing, it's a medical Best Practice thing. Many countries, like Canada for example, have used sprays and sub linguals for years, all at high levels..
But the NHS bolloxed it up and the real objections, like there are no tablets that have been through the drug testing procedures, means that people like me have to take a punt and hope the manufacturer is honest!
The idea is that you have your injection as usual, then take a tablet a day until your next injection date arrives. Then you have a blood test and see if the tablets are working. If they are great, if not back on the injections.
If the tablets work then you won't feel worse, they work better than the injection as there is no slow wearing off. As long as you take the tablet your levels stay up and level. The massive daily overdose in a 1000mcg tablet means that the vast majority of people without the intrinsic factor for B12 will get just enough of the B12 crossing the blood barrier to keep their levels up, just 1% by passive absoprtion is enough.
After 20 some odd years of the injections. I was alarmed at first but did some digging. The PA Society has taken a hard line in its information, sensible but quite scary. They have recently updated their guidance, so I am currently looking at other supplements. I know the tablets work so sub linguals etc should be fine too, if far more expensive than the tablets I am currently on.