How could you dress this down? for day wear, if you don't have a leather jacket....

[Newhere2]

its a great fitting dress, hides everything!
[http://www.allsaints.com/women/dresses/allsaints-marilla-dress/?colour=21&category=4681 dress]]

dress

It's a lovely dress, It looks clingy in the picture but if not in real life then it's a winner. I might take a look.
Dress down with a denim jacket maybe, wear over footless tights with trainers or black/grey converse type shoes. Marl cardigan or cropped jumper or sweatshirt over the top.

The grey version looks more casual

hi cromwell, it does 'fit' but the stomach feature really hides everything, even after a big meal :)

demin jacket and leather trainers maybe?

morello, yes the lighter colours are more casual, I almost bought 2 :)

I got the ink.

trainers, brogues, sandals. Denim jacket or cotton/linen biker jacket. I have something similar from TopShop which is very flattering and I get lots of wear from it.

It looks lovely and is that colour I see? At All Saints?

I would just make sure that everything else is casual so yes to denim jacket or a cardi (maybe cropped so it doesn't spoil the ruched bit) flat shoes or ankle boots, chunky jewellry, minimal make up, messy hair etc I have something a bit similar and I sometimes wear a long-sleeved T underneath although that depends on the neckline.