Soooo difficult to tell! Loads of things may have contributed to it, I think:
1) The fact that they said a 'high 2.1' was required and stupidly didn't specify a number between 65 and 70, plus the fact that my transcript was so difficult to follow (the guy looking at my transcript admitted over the phone that he didn't understand it and that basically all he could see was that I got a 2.1)...
2) Good references possibly (I made sure I got people who really liked me + who had a lot of clout to do my references, including one guy who's an internationally renowned classicist who told my tutor he was impressed by me the first time he met me in my first year...ugh, that sounds so boastful. My apologies

).
3) Very careful choices of what pieces of work to send - I sent a piece that got me a 75 in the second year and a piece that I presented at a conference at Exeter in my first year.
4) I emphasised the fact that I'd been hobnobbing at academic conferences since I was 17 and generally being a bit of a geek (ugh again...sorry

). I didn't mention that earlier, actually -
going to academic conferences as an undergrad, even if you barely understand a word that's said there, probably looks quite good when applying for postgrad.5) I have published, but only in internal journals at Exeter and in one very little-known national journal that's mainly for teachers in schools rather than for university academics.
They didn't interview me so that's basically what they had to go on. Oh, and you have to write a personal statement, of course.