In my experience it very much depends on the institution. I did my undergrad at one of the Oxbridge colleges, and it was very clear you could fail if you eithe

In my experience it very much depends on the institution. I did my undergrad at one of the Oxbridge colleges, and it was very clear you could fail if you either weren't clever enough or didn't put in sufficient effort. If you turned up without having completed the work they just sent you straight back home with a black mark that counted against you when you failed the exams and wanted another go. Exam questions basically only awarded 33% of the marks for "bookwork" and the rest required you to demonstrate an actual mastery of the topic. My grad school was at a Russel group school (the tier just below Oxbridge), and it was clear that the undergrads there could just coast as long as they handed something in. If they turned up to a tutorial without having done the homework there were very few consequences. If you failed the exams there was an automatic retest in the summer. If you could regurgitate your text book you would probably get a 2:1.