Well I'm (going to be) a 4th year chemist, have quite a few friends in engineering, chemical engineering.
Honestly, amount of work varies. Not only on the subject, but also on the person - their capabilities, their personality, etc. Some people are perfectionists or take great pride in all their work, even if its only for a supervision. Others (like me) believe that doing the minimum required is best so you can go and do other things. Engineering is of course a reasonably conceptual course - some people pick up and learn new things faster than others. These people get more free time. Some people really enjoy their work, some gradually start to get annoyed by their degree. There's also different philosophies. Whilst, I think, most people put work as their number 1 priority, some people have sport or another extra circular as their top priority and try to fit work around that.
Let's talk numbers: if 3-4 A-Levels is roughly 20 school hours + 6-7 homework hours (per week) and then revision might go up to 40-50 hours. Then I think even doing the minimum for a degree is probably more than this. 1st year natsci is 40+ hours to do the minimum, and obviously if you are struggling and need to read notes again or go over things more then this will go up and up. If you are efficient, you can probably bring this down to 30 or so, but it's definitely "more" than school. You don't really have a day off work unless you are very good and efficient about doing assignments. Sometimes, your workload can spike or you missed some stuff and are trying to catch up or you have something important due in, or you are really struggling with a topic - in this case you might spend almost all week doing work.
So yeah, depending on how clever/efficient/hard working/ how little you care/how many hours sleep you naturally need it's probably between 25-45 hours a week. 25 would be naughty, 45 would be excessive for most people (probably struggling to understand and needing extra time). Even a conservative estimate of total time is closer to 80 hours a week, so there is plenty of time for socializing and sport! But you have to be sensible. If you have 2 lectures + a workshop + a supervision tomorrow, you can't really go clubbing. Also, there might be a party later, but you've spent the whole day doing work so you might be a bit down. Going for a rowing outing might mean you miss the first 30 minutes of a lecture (this is probably fine though). Inevitably, you will find some good friends within your course because of how your time is divided.
The key word in cambridge is efficiency (and probably damage limitation). You have 12 (difficult) problems to do - avoiding procrastination means this could maybe be less than 3 hours. But I've known people who get stuck (if you are badly stuck, move on) or spend the whole day at their desk "doing work" which should have been done ages ago. Another common scenario is you have 2 hours to do something which should take 5 hours - in this case you need to learn how to make it look like you put 5 hours work in
This is the skill i am most proud of having.
I may have painted a negative light of cambridge here. There is a reason terms are only 8 weeks long. By week 6-7, most people have had enough of work and are drained. At the end of week 8, it is common to go home and just sleep for a few days. Most of my friends would say they love and hate cambridge