Quick Brit Speak Question: 2:1 in his MA

[Steve]

Read a recent article about Prince William who is about to graduate
from St. Andrew's University in Scotland.

The article said something to the effect that he (William) is expected
to get '2:1 in his MA'.

I assume 'MA' is Master of Arts, but could someone explain the '2:1'
part? 

ITV Article-
http://www.itv.com/news/504655.html

Quote: "...he is on course to achieve a 2:1 in his MA."

Just curious.

Steve/bboyminn