I don't have that specific dress, but I just ordered a TON of stuff from Delias assuming that it would run small - but it didn't. It ran TTS and big. i had to send everything back.
Yup, that's me! I love that dress. Thanks for posting it again, rosie--you just reminded me that I have it and I need to wear it more!
Anyway, I think it runs pretty true to size, not as small as I would have thought. I'm usually a 6/8 and I got a medium and it works fine for me. The mandarin collar is a bit more pronounced in person, but it's still a very versatile dress. I've worn it to work with black tights, black boots, and a black blazer and I think it'll be cute in the summer too with casual black heels.
The quality isn't fantastic, but for a cheap dress, it's not bad.