Even though this is old thought I'd write for anyone searching about Sainsbury's later.. they give you a polo shirt, trousers, jumper or fleece and you can wear your own shoes unless you request the hard toe ones if your working in an area where your toes could be at risk. You just have to wear dark shoes (eg black, navy blue) they can be trainers or normal shoes but no unsuitable heels, sling backs or ones with no sides etc. It's common sense really.
I'm like 5ft1 and size 6/8 and the tops and stuff are all men sizes the XS is huge on me! lol but they have different length trousers which fit me and they gave me size 8 which is a tad loose but they do. They are ugly men things though lol and come right up high on the waist. I despise them tbh!
You aren't allowed to have loose hair while working (unless its too short to tie up), nail polish on, earrings that aren't studs or sleepers, rings that aren't wedding rings, bracelets, necklaces, etc. Minimum makeup is mentioned too but I think your ok with makeup aslong as it's not heavy and obvious like big red cheeks, black eyes,..