Daily Sports is generally a closer fit product and the choice of size depends on how you like to wear a garment. They tend to be quite shaped and ladies with a bigger middle area may prefer to go up a size. Generally a size XS would equate to a UK 8 and goes up to an XL which is an 18.
Glenmuir and Anika are a more generous fit and therefore a XS would suit a size 10 to fit the body shape up to XL which would be great for an 18.
There is lots of stretch in most of the products.