If contemplating undertaking an MSc course in the UK, how important do you think it is that the course is accredited by an external body?
Do you think it's something future employers would take note of?
Or is lack of accreditation something that should not give prospective students concern?
Accreditation (in engineering) will lead to becoming chartered. I'm not sure about other STEM subjects, but in engineering it does have some relevance. It is not the end of the world if it is not accredited, but if that's something important to you, consider finding a course which is accredited. You could contact the appropriate body to check with them too.
Employers probably won't notice as many are not accredited. There seem to be more which aren't than are.
You need to tell us what subject you're considering. In engineering accreditation (even at MSc level) is quite a big deal, and some employers won't even look at your application unless you have an accredited degree.