I only recently discovered that ASOS has a plus size range called Curve, which does UK sizes 20-26.
www.asos.com/Women/Curve-Size/Cat/pgecategory.aspxI can report that the t-shirts, leggings, belts and skinny jeans all fit well.
AND they have a real leather biker jacket. I've been looking for a non-middle-aged-looking one for AGES in my size. Apparently most shops believe that if you're over a size 18-20 you will be needing a blouson-style elasticated-waist leather jacket that makes you look like an off-duty copper or a model for those magazine pages that sell "stylish slacks".
Now all I need is the balls to wear it as it's a bit scary (and for no-one to take the piss or point out that it's passe... I am fortified by noting that AllSaints, where I would buy all my clothes if I could, are featuring biker jackets again for this Autumn...)