Honestly, A-Levels was the most unpleasant experience of my life. Pressure from teachers, intensity of 3/4 courses at once etc and at a young age (16-18 for most). University life was more me, much more pleasant and it's a much better environment to learn. HOWEVER, it is not easier, but rather different and more developed
At undergraduate, the amount of analysis is more intense, length of essays will be longer but for me this was a gradual development and you won't notice it too much if you're first year is taken seriously and taught well.
However the main jump is in reading. I was basically given 2 books minimum to read a week, closer to 3-4 with a lot of supplementary reading. Most schools / sixth form colleges have no where near the amount of reading, i mean no where close, or maybe my course was just quite intensive.... I was only in for 10 hours a week in my last year but was reading probably 30 more (i was a bit of an anorak and im not that clever so I had to do every bit of work to develop my grades)
The other hard part of undergrad is that (at least on ym course) it was very seldom they would look at any draft of your work. For this reason, reading feedback is SO important. So if you get 60% (the 2.1 cut off) and you want to improve, you really have to re-read your next essay and almost check off the feedback (if relevant, different tutors mark differently) to make sure you've developed to the feedback. Finally, you will need to choose modules you will enjoy, not just because your friends are doing them. Doing 3/4 modules at once is tasking, but if you enjoy them all then it is much more rewarding and enjoyable
Things that are easier is that the first year is an unofficial "trial period". Money aside, from an academic point of view in the UK VERY few courses mark first year students. Nearly al institutions grade 2nd and 3rd year (mine was 100% 3rd year marks or 60% 3rd year /40% 2nd Year depending on which averaged higher). Thus, you have the time to get used to the workload, not have teachers tell you you have to undertake 5 volunteer jobs or you won't get into your insurance uni choice etc.
they key thing is love your subject, work hard and you'll be fine