I didn't get very far with lacing the front wheel, so on the basis that the only stupid question is the one you don't ask, I popped around the corner to see Bill, a chap in his eighties who has been restoring veteran bikes since before I was born. Bill who soon pointed out my beginners error. When I unpacked the spokes, the rear spokes were in two bags. I did check to see if there were any differences but they were the same length and had the same angle of bend. So without further thought I got stuck in. Bill pointed out that I had two different spoke sets, one of which had a slightly longer bend, these should be used when a spoke crosses on top of another at the hub. Mystery solved, he kindly offered to finish the wheel for me and true it up, in the meantime I admired the last of the three 1920s Sunbeams he'd restored, from being piles of rust dug up out of ground of a old scrap yard. Not to mention his Velocette, Vincent Rapide and a couple of specials.. I must remember to take my camera next time I visit.