I'd say it's a very different ball game to getting A*s and As at A level. Working hard has much less to do with getting a good grade at uni, and you will benefit much more from working smart. Dare I say that in my cohort I've seen more hardworkers on the low and middle end of the grade scale than on the top end.
If I had to pick the best predictors for getting a 1st class they would be going on a year to North America or doing a Year in industry. Granted, these are somewhat self selecting groups, but I would say they're still valuable as predictors. This year I've seen a few people come back from these years and in particular for the year in North America group their grades have skyrocketed. They've developed a much more reliable and constant work ethic, which I would say most people find very difficult to do without being forced to.
I would also emphasise that getting a 1st won't make a whole lot of difference over getting a 2:1 unless you want to study a master's course at a particularly competitive university (e.g. Imperial/Oxbridge) or a PhD. Even then, for a PhD if you have good research experience then you can manage with a good 2:1. Otherwise your project and internship experience, alongside whether you're someone that people want to work with, will be much more valuable on your CV. To give examples, I've seen 3 people with grades of 85-90% struggle to get internships while others with ~65% have had offers thrown at them. 2 of those 3 people didn't have any experiences outside of the course, and one of those managed to get an internship in the end but it was at a company who gives everyone from our uni internships. The third person had some fantastic experience running large projects at uni, went on to get a summer internship, but despite wanting to move to another company for his YINI, was unable to and had to stay with the company he did his previous internship at. Another person who was on a first didn't get their YINI until late into the summer.
Basically, don't overvalue your grades. Make sure you get a 2:1 first and foremost, then make yourself someone who is good to work with, then get involved with good projects and activities (usually the more practical and competitive the better, e.g. Formula student will always look fantastic), and only after that should you worry about getting a first.