For a variety of reasons, I had to withdraw from university prior to completing an undergraduate degree. 25 years later, I've managed to carve out a successful career in accounting and finance, doing interesting work in senior finance roles based in Asia-Pac, Europe and the US. I now find myself in a position where I'm looking for a new job, but my lack of an undergrad degree (or an MBA for that matter) is a limiting factor in pursuing the career opportunities I'd ideally like to.

I'm looking at UK based online MBA programs, and it appears that I may be accepted based on my professional accomplishments and experience, regardless of my lack of an undergraduate degree.

My first thought was that having an MBA qualification would likely supersede any requirement for an undergrad degree, and put me in a position where I can apply my experience as well as the knowledge gained in earning the MBA degree, and move forward with pursuing the types of career opportunities I prefer. However someone mentioned to me that the lack of an undergrad degree might still be an obstacle, even after earning an MBA.

Assuming a good school and reputable MBA program, does anyone have a view on how much / little employers may care about an undergrad degree once an MBA degree has been completed?

No-one will care about your lack of an undergraduate degree if you have a good MBA.

indeed employers will not really bother with undergraduate degree from someone with 25 years of work experience. At this point your experience will trample everything else. So MBA or EMBA is the only reasonable choice

If however it bothers you too much, Leicester and Queen Mary offer a diploma in addition to their MBA, so your MBA won't feel lonely in your CV
However you really should consider some better MBA, or EMBA options first - diploma or not! The rule of thumb is to always aim for the best MBA you can be accepted to

P.S. accounting is exception, in some countries you really need a degree -by law- to work in accounting

While Leicester and Queen Mary are decent suggestions if you need a separate diploma, there are probably better options out there. You could probably just contact schools in the UK to ask if they require an undergraduate degree to get into, and I'd assume that many (most?) will make exceptions if you have a lot of work experience.

Some good discussion with schools here:

https://find-mba.com/board/general-forum/mba-without-undergraduate-degree-52736