I tried them on and they fit fine. A little snug around the tops of the thighs, but I think that's the Lycra slimming thing (the thighs are the same as in the regular Spanx, and those do the same). The belly and waistband are super-comfortable--nice support from underneath, no pressure on the stomach, waistband doesn't roll or bind. Heck, I'm more comfortable with them on than without. :)
The nude is a little dark, but I have very light skin so I can't really complain. It's another reason I usually like Nordstrom's own-brand hosiery--they do multiple shades of beige and the lightest one is great on me. Still darker than my skin (which, let's face it, is closer to ivory!) but flattering and non-jarring.
I still can't believe I spent £20 on non-special-occasion tights, though. Extravagance! But then, I suppose that given the load I am/will be carrying, it's not an entirely wasteful indulgence.