Can university impose new degree classifications on a whim?

What if they lower it so getting a first class degree is super easy and no one checks? It would be a smart way to boost graduate prospects, until the competition figured out and ruin them I suppose.

Surely having cohorts with too many firsts would give a negative image of the Course/Uni? Having a stable number (ie 10-15% on average, all other things being equal) would make the degree in itself more valuable in the eyes of the employers?

If more people get firsts then they're (theoretically) more likely to get a grad job and therefore the university looks better because more grads are getting employed.
It depends on how they look at the figures.

I don't see why they would randomly change it though.

Say a first is raised to 80 and the pass mark is raised to 50. Isn't that unfair to the students at this particular institution since other places keep the regular 70% for a first and 40% for a pass mark?

Given that universities need to be accredited by the government in order to function as higher education institutions, if a change was made that damaged the university's integrity then I guess they'd do something about it. Universities aren't free to do whatever they want.

afaik Unis don't normally make changes to running modules till the end of the year, even if the QAA is breathing on their neck.

no reason why it'd be wrong for a uni to set the first level at 80% providing it wasn't a goalpost move on students part way through - e.g. afaik 80% is where the OU has had it for years.

Why do we have the wide first-class band?

Presumably, the committees that determined the canonical marks boundaries had reasons for their choices. However, whilst the decisions have been passed down to examiners and tutors, the rationale has not, as far as I know. One can only attempt to reconstruct how this division was supposed to work.

The central idea appears to be one of rewarding excellence, even if that excellence is patchy: a student who does something outstandingly good, even at the expense of other work, should have it recognised. Thus (to take an extreme) someone who consistently gets 69% receives a 2i, but someone who scrapes by with 45% in half their units but gets 95% in the other half receives a first. In general, a mark in the 80s or 90s cancels out quite weak performance in other units regardless of the student's final mean. Of course excellent students often perform well all round - but there are always many borderline candidates for whom these biases in the marking scale can be highly significant.

Say a first is raised to 80 and the pass mark is raised to 50. Isn't that unfair to the students at this particular institution since other places keep the regular 70% for a first and 40% for a pass mark?

Put it this way; when I went to university, the degree classes at my university were 1st, 2nd, 3rd, pass, fail.

Part way through my 3rd year, they changed it to 1st, 2:1, 2:2, 3rd, pass, fail.

Lots of people who thought they were going to get an undivided 2nd ended up with a 2:2.