In reply to masa-alpin:
Tech grade simply speaks about the physical difficulty of the most difficult move on the climb done in the (currently known) easiest way and without consideration of any other factor.
The adjectival isn't an onsight thing either in reality (this is a contentious topic). It simply combines how many hard moves, how sustained, how serious the fall etc etc in to one grade.
So no, in the example you give the adjectival grade won't necessarily be high for the route you described. It would only be high if that 6a move is above a serious fall, or there are lots of 6a moves on the line etc etc. You get the drift. The fact it's blind makes no difference to the UK grade. It may just say "difficult to onsight" in the guide.
Post edited at 20:47