I vote for a "Constructeur" also. I recently purchased "The Golden Age of Handbuilt Bicycles" by Jan Heine and your bike has a lot of features of a Singer, although I don't think it is. You should send an email to Mr. Heine at Vintage Bicycle Press
www.vintagebicyclepress.com as he is incredibly interestested in constructeur bikes.
I have a pair of Reynolds "Hiduminium" handlebars that are stamped "Made in England" also.
Amazing bike! I cringe a little bit that you tore off the original leather handlebar wrap, even if it was rattty. If the bike was a "Herse" or even rarer builder you greatly devalued the bike by changing anything at all.
Good luck,
vjp