how much difference does getting a 1st actually make?

I've heard that some employers actually prefer a 2:1 because it means you've had a life as opposed to locked yourself away and studied throughout your entire uni experience. That's not me saying that for anyone who disagrees, it's my teacher, who has a 2:1 so she's slightly biased anyway

It sounds like she had aims for a first herself, and is now trying to justify her own failure

I've heard that some employers actually prefer a 2:1 because it means you've had a life as opposed to locked yourself away and studied throughout your entire uni experience. That's not me saying that for anyone who disagrees, it's my teacher, who has a 2:1 so she's slightly biased anyway

It's personally made no difference to me, not getting a first. I pissed around half of my time as an undergrad, did just enough work to get a 2.1, and am now doing a PhD in one of the best universities in the world. If I had spent a bit more time on essays, and done more revision, I could have got a first, but partly because I am lazy, and partly because I was distracted by socialising, I didn't fulfill my potential. If had got a first, then I would probably be doing exactly what I am doing now. I know if I had got a 2.2 I would have been screwed though. I do slightly regret not doing enough work, but there is still plenty of time in the future to prove myself. Getting a first is one way of proving yourself, but in a long academic career, (which I hope to have), there will be more important ways of doing so.
If your undergraduate degree is the only degree you ever do, then I imagine the disappointment of not getting a first will stay with you for longer, and will be more of a blemish on your CV. If you get a PhD, then people, including yourself, aren't going to care as much.

I've heard that some employers actually prefer a 2:1 because it means you've had a life as opposed to locked yourself away and studied throughout your entire uni experience. That's not me saying that for anyone who disagrees, it's my teacher, who has a 2:1 so she's slightly biased anyway

Lets ignore the 3rd year degree classification but your first year degree classification makes a huge difference between getting into summer internships in Investement Banking, Management Consultancy, Corporate Law and Diplomacy.

Work as hard as possible straight from the first year, even if in your first year degree i.e. like Oxford, does not count towards your fiaal degree classification.

No offence pal, but I wouldn't call St Andrews 'one of the best universities in the world'.

Nor would I, I'm at Cambridge.

I'm not sure it makes any unless you're applying to very competitive postgrad courses. I've not come across any graduate schemes or jobs that require a first and exclude 2:1s. Sure you could say they may look at someone with a first more favourably, but I find it's the skills you've gained during your degree/life that they care more about than your grades when assessing your suitability.

Now the difference between a 2:1 and 2:2, that's massive and will rule you our of a lot of jobs and graduate schemes. But it's not the end of the world for you if you get one.

Funny enough, the thing hindering me is nothing to do with uni, it's the fact I went to uni with the equivalent of two A levels rather than 3 (mature student). You're ruled out of a lot of graduate schemes/jobs if you don't have over 300 UCAS points regardless of whether you get a first or even 100% mark on your degree. It's silly but they need a way to throw many applications in the ein before looking at them and that's the easiest way.