Are New Look sizes bigger?

Are new look sizes bigger because I bought a size 10 jeans from Jane Norman and my friend has a bigger bum than me and has managed to squeeze herself into a 6 from New Look? I swear they must be bigger. Can anyone confirm this? And yes before you say it, I'm a stay skinny, small size freak but I'm not anorexic just to clarify that. And she also gets jealous about other people's sizes as well.