The British system is a mystery to me. I remember telling myself when I started my degree (outside the UK) that, unlike school, all that mattered at university was whether or not you passed and ultimately got your degree. I never aimed any higher than passing.
"Just passing" wasn't a trivial achievement, 50% of first year physics, chemistry and Maths students were failed, meaing they'd wasted a subject-year. Many of the people failing had top marks in the same subject at school. People who passed Maths were told not to bother going on to second year Maths Major (their were lesser maths courses for teachers and engineers) unless they intended to do postgraduate Maths. This put off enough people that relatively fewer failed second year. (There were maybe 150 people doing Maths 1 major, by third year we were down to a class of about 15.)
When I arrive in the UK a year and a half after graduating and heard people talking about grades, I wondered if I'd been mistaken about grades mattering. When people asked me about my grades I said I didn't know, that the system was different. I don't think it made any difference to my career.
My degree certificate says nothing about grades. You either got a degree or you didn't.
The only distinction I became aware of was that if you scraped a pass, you might not be allowed to continue in that subject. For example, I scraped second-year statistitics, and was told I couldn't do third year. (Had no such intention anyway.) I passed third/final year mathematics with quite a low grade, but could have gone on to do post-graduate maths if I'd wanted to.