Hi vickyclare,
What a dilemma!
If you went to school in GB, it is a common practice to test all pupils for TB around the age you stated. I cannot think why the "powers that be" do not believe you, unless of course they think that you tested positive. Whilst at school, I had this test along with all my classmates. I tested positive (along with a chum of mine), as did my brother and another lad. We had to go to a hospital to have lung X-Rays to check if we were carrying the disease. Luckily we were not, but the reason why we showed as positive was because it meant we had been in contact (at some stage in our lives) with someone who had TB.
All this was explained to us as to why we did not need the BCG. I suppose it is like having become immune because of the earlier contact.
I hope you get this all sorted, but if you have to have another BCG I cannot think this will be harmful to you.