Well, it's not much, but this is what I know.
A man in Australia has an old anglo concertina, says "Made in England", and "by C. Staff", but there is no 'brand' like Lachenal or Wheastone to be found.
The fretwork, from what I can tell, looks like a Lachenal, but the pictures are at an angle. I've asked him for a face-on picture of the fretwork.
Does that give someone any idea?