There is currently a marked Davidson lidded container with matching underplate on ebay which is very similar in shape to your "Greek key & daisy pattern" lidded jar, but the ebay piece is decorated with Davidson's RD 340825 (registered 5 July 1899) pattern:
http://www.ebay.co.uk/itm/322405342870?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITThe size is given as "standing at 20 tall with a 19cm wide stand" so I suspect that this is a biscuit jar / barrel.
Chris, from the size you give, I suspect that your 'barrel' is a honey or marmalade jar. In fact, Davidson shows 2 honey / marmalades in their catalogue of unregistered designs (patterns #522 and #529) with a similar shape and finial to your piece (though they are not shown with an underplate). I have not seen a similar piece in this pattern before.
Page 108 of the Stewart's book - "Davidson Glass ; A History" has an illustrated advert with the Davidson 'Daisy' suite from a Supplement to the Pottery Gazette dated 1 December 1886. The list of pieces in the suite does not include a honey/marmalade or biscuit barrel, but I have come across several other shape decorated with 'daisy' pattern that don't appear in the list either.
I have to go out shortly, but I will post pictures of the #522 and #529 honey/marmalades later today, and I will contact the seller of the RD 340825 biscuit barrel seeking their permission to show some of their photos on this site as permanent references in due course.
Fred.