Many thanks to all the readers who posted replies to my conundrum.
I have distilled two distinct schools of thought from the feedback:
1. Accept that we are destined to be 'good friends' and leave it there.
2. Go for the relationship but accept that sex is not an optional part of a deal.
Obviously, I shall take some time to reflect fully on these suggestions. However, my immediate reactions are as follows:
Regarding solution one (the 'good friends' paradigm), I am concerned about the intensity of my feelings. Far more sharp than I usually have for a friend, male or female. Such extreme intensity I can only associate with love. However, my experience is perhaps somewhat limited. Perhaps it is normal to feel such intensity with a very close friend? I don't usually discuss my emotions with friends - although I have with this woman - perhaps this is why I feel so strongly?
Regarding solution two (drop the no-sex rule), I am concerned that I could end up hurting this lovely woman if I try for it but fail to follow through. I imagine that sex requires some active physical intervention from the male partner. (I suppose it's a bit easier for the female partner who can 'lay back and think of England' if she is not especially interested.) It's a real step into the unknown and I am going to feel very irresponsible if I recklessly charge ahead only to give up later saying, "Sorry Luv, you're not really my type".
Furthermore, there's also an element of pride to my losing my virginity. Although I'm really not bothered (honestly - I'm long past worrying about it), after all these years of chastity I would prefer to lose it with a woman I find sexually attractive at least. Otherwise, it seems a bit silly to expend 'the one perfect moment' on a woman I would rather not be having sex with.
Thanks again to everyone for the replies. My thinking is now somewhat clearer: now I perceive two distinct options.
Being a forum in cyberspace, I knew no one here knew me from Adam, so I know my anonymity is effecatively guaranteed. Late last night, when I decided to throw in my scenario on a whim, I didn't really expect any serious replies. Tonight, however, I am genuinely pleased with the commentary I have received. Many thanks to all readers who posted feedback.