the jug shape of the body isn't identical and the handle doesn't have the thumb mark on it, but it's very close.
And interestingly I found two jugs in the Harrach book that have the tri-shape rim and the inside edge applied handle page 145 and 102. They are larger jugs and different body shape but both opaline glass and date to c1845 and 1842. The link between those two and my jug is that going back to my original post, I wrote this:
'My searching brings up a jug (different decor but on opaline glass) that appears to have a similarly applied handle and shaped rim and with a rim that curves down at the front spout, that is attributed as probably Baccarat - it has a hand enamelled mark on the base 'P and then a number'. '
The link I gave to that piece has gone now, but that way of marking is seen on Harrach pieces (with the caveat that I have one piece that is similarly marked and is in question over whether Loetz or Harrach still - shape not matched to either maker)