Originally Posted by
unworthy1
definitely does and says that these are Imperial size tubes. Therefore, 99.9% certain that it's NOT French despite all the FR frame components. I'll still bet it's made in the UK and probably has had some braze-ons added later in life when it was undergoing a re-spray. Don't know why it has the 26.2 seat post since it seems like this should be a frame constructed of all 531 DB tubing...but, there you go. Still couldn't even guess at a builder's name but it's clearly a high-quality frame and deserves the best treatment.
Agreed, it's probably British but I don't necessarily agree it should be a 531DB frame. The frame is boom era or older. At that time 531DB was pretty much reserved for top end racing frames. There was a belief that butted tubing was too light for everday usage, given road conditions. Grand touring bicycles of the day were usually straight gauge, unless custom built, as were most mid-range racing bicycles.
Of course we can't dismiss the possibility of a sleeve but that should be easy to check. The head of spoke, inserted into the seat tube, should catch on bottom edge, when dragged up the tube. Alternately, there's the possibility that the 26.2mm post is actually undersize and the lug has been pinched int he process. The quick check for that is whether the cinch slot is narrower at the top than the bottom.