The educational discount is around 15% for Higher Education (e.g University) and I think its around 8% for Further Education (e.g College) and other educational establishments.
Pretty certain on the 15% as I asked someone at the apple store today when I was looking at a macbook pro. However, the 8% I can't be entirely sure on - Pretty certain it was this two years ago, not sure if it has changed.
You can use this link
http://store.apple.com/uk_edu_78186/ to see the prices at Higher Education, without being connected to a university network :)