You need to know the institution; some are much better than others. In the UK, the "Russell Group" of universities is a good starting point, followed by universities with towns in their name, and be suspicious of universities with vague regions in their names (South Bank, Thames Valley spring to mind). There are, of course, honourable exceptions (West of England springs to mind).
Beyond that a decent degree or lack of a degree is a strong bias in certain aspects of competence. Whether those aspects of competence are relevant to any particular job is for a company to decide. Whether any particular candidate has the necessary skills needs to be assessed at interview.
Summary: a good degree is a sensible bias, and the lack of a degree another bias. But neither are absolute.
Analogy: if someone is choosing your course of medical treatment, you really want them to have a relevant degree. Similarly, if someone is sticking a needle in your vein to take blood, you want them to have relevant (but different) qualifications. Even then, you get notably bad doctors and notably good nurses.