Some photos of a decanter RD 736240 (with what seems to be the original stopper). 25cm tall (including stopper) and with a base diameter of 10.5cm.
(Permission for the re-use of these images on the GMB granted by chictat).
Two water jugs from Idris & Co. registered designs were discussed athttp://www.glassmessages.com/index.php/topic,21289.msg299306.html#msg299306
More information on Idris & Co. athttp://www.gracesguide.co.uk/Idris_and_Co
By the way, there was a well-known television jingle advertising Idris lemonade from the early days of commercial television (1960s?) that went:
“I drink Idris when I’s dri,
Idris is the drink to buy,
I drink Idris, I drink Idris,
Idris when I’s dri.”