Some time ago Mickey Walker asked about "the earliest known film footage of an Old Firm game."
The answer I gave was "The earliest I've SEEN is the 1928 Scottish Cup Final. But if anyone out there knows of any earlier, please get in touch with the address at the top of the page.
Mickey has e-mailed to say "I have now seen a 1921 clip of a Celtic v Rangers which I think is a Glasgow Cup Final."
The earliest Scottish club match I can find on Pathé is the Thistle - Rangers Scottish Cup Final from 1921 as well though I'm fairly certain there were pre-WW1 matches filmed. Whether any footage has survived I don't know
