I had a great personal shopping day with a client yesterday, trying to find her a mother-of-the-groom wedding outfit. Because my client is a size 18/20, we went to the Watercolours Fashions shop in Beaconsfield, South Bucks (http://www.watercoloursfashions.co.uk), which specialises in sizes 18-30. If you fall into the larger size clothing category then you MUST check it out!
There is a fantastic choice of colours and styles, so whatever season or personality you are, you are bound to find something that fits AND is interesting. It is so refreshing to see such a lovely choice in the large size clothes, which usually tend to be on the boring side - not unlike bigger size cup underwear, which is my bugbear (see http://www.bravissimo.com) for inspiration). There are 25 different designers to choose from.
The staff are very helpful . There is a price range to fit any budget, but if you are looking for something special, you will have to part with a bit more. It is definitely worth it. The shop also offers funky accessories (jewellery, handbags and belts), which are definitely worth having a look at, too. Have fun!