[tonyedgecombe]

I'm not sure about Oxford but certainly for Cambridge you aren't graded overall, instead you get a grade for each part of the tripos[1] (two parts).

https://en.wikipedia.org/wiki/Tripos

[NPDW]

Yes but you generally treat your degree as being graded by whatever you got in part II

[ianopolous]

In Oxford, at least for Physics, your grades from every year (except possibly the first) count, but they are heavily weighted towards later years.