Ooh, defensive! Well, doing some googling suggests that 2% would be the lowest estimate, 10% seems to be a common estimate, 20% being the highest.
Personally I would say 10% sounds about right. If I went to say London and picked 100 adults at random, I would expect about 10% to be homosexual, and I would be really surprised if only 5% were. I would also guess that if I picked 100 adults between 16-40 from the same place, it would go up to about 15-20%.
Of course there'll be quite a large regional variation, particularly in areas where even in the 20th Century, gay people still ran the risk of being strung up or imprisoned for it, or at least ran the risk of losing their livelihood or the support of their family. This would also seriously affect any statistics gathering.