Well, based on feedback so far, I shall try to find the thread markings on the Allegro HS to determine if perhaps it is in fact an English HS but with a flatted steerer as evidently was common with Raleighs of the same era. This would make the 22.2mm stem a bit less strange, though one then asks why the Swiss used Swiss BB thread, identical to French save for the left hand fixed cup, yet used an English steerer on the same bike.
As to where the Pros and Internationals were made, all I can gleen from the RetroRaleigh site is that all Raleigh 531 frame production (presumably including the former Carlton models) was supposedly moved to Worksop when Raleigh bought Carlton in 1960. In 1974 "Speciality bike" production was moved to Ilkeston, but that apparently did not include all Pros and Internationals as some apparently were subsequently given serial numbers beginning with "W", designating Worksop. Even presuming all this is true, I imagine there is much more to the story. Perhaps Hilary or another UK member familiar with Raleigh history can enlighten us.
> Quoting Jerry Moos <firstname.lastname@example.org>:
> > Do such Raleighs have a flatted washer or did they just let the keyed
> > washer
> > butt against the flat? (This does work but isn't very elegant). With
> > the
> > Swiss reputation for thoroughness (Swiss watches and all) you'd expect
> > them to
> > be a bit more exacting than the lads at Nottingham. Speaking of
> > Nottingham,
> > were Professionals and Internationals ever made there, or were they
> > produced
> > only at Worksop and Ilkeston? If the latter, are they usually free of
> > the
> > indifferent quality sometimes observed in other Raleigh models?
> > Regards,
> > Jerry "haven't owned a Raleigh since my wife's 1977 Grand Prix sold a
> > couple of
> > years later" Moos
> My '71 International has the flat on the steering column, and I think my '74
> International has a key (don't recall for sure). I thought all the Carlton
> models were done at Worksop. Were some of them done at Ilkeston?
> Regarding Raleigh quality, I prefer to think of it as "character"! Or an import
> ban on small files. I can't decide which.
> Steve "irrational Raleigh Lust" Kurt
> Peoria, IL