Thanks for that; I don't have access to Fleischmann. This is another example of the earlier form of the tune, and so far the earliest we have. Bruce Olson's indexes list this as Caledonian Hunts Delight/ Favourite Irish Air; is 'Favourite Irish Air' the sole title given in the MS?

Olson put the date of NLS MS 3346 at c.1765-75, but I don't know how he arrived at that. He was certainly critical of Fleischmann's approach to dating.

Further to my earlier comments on the 'Fiddler's Companion' reference to John Glen, it would appear that he actually dealt with the tune both in Early Scottish Melodies and the earlier Glen Collection of Scottish Dance Music. A footnote in Alfred Moffat, Minstrelsy of Scotland (2nd edn., 1896, 278) to 'Highland Mary' (there given the main title 'Ye Banks and Braes' from its opening line) includes the following:

'The claim which Mr Chappell puts forward in Popular Music of the Olden Time, for the tune being English, has been well met by Mr John Glen, of Edinburgh. In the excellent preface to the Glen Collection of Scottish Dance Music, Mr Glen points out that as early as 1687, the air was published by John Playford, in his Apollo's Banquet, as "a Scotch tune".'

The air referred to is 'Katherine Ogie', not 'Caledonian Hunt's Delight'; the latter appears as the next song in Moffat; also with a footnote indicating that Glen disposes of Chappell's claims in his preface to the Glen Collection. On the face of it, it looks as if someone has confused or conflated the two references; but it would be necessary actually to see the book (ideally, both), of course, in order to be sure. Early Scottish Melodies is listed by Google Books as digitized, but if it is online, access is denied to UK-based users; although it is just as much out of copyright here as in the USA.

Leaving aside the point (made by Chappell, as it happens, but not uniquely) that in Playford's time 'Scotch', as applied to music, was a generic description rather than (necessarily) an indication of origin, there are still several potential antecedents in Apollo's Banquet that need to be looked at, if only to discount them. Does anyone have access to these? Incipits and stress-notes are provided at Early American Secular Music and Its European Sources, 1589-1839: An Index, but I lack the musical knowledge required to make anything much of such things.