Hi Andrew,
I am sure this topic is fine and may well interest other BAA members.
I can’t answer your exact question, but I have experience which may be relevant. I am a part-time self funded mature Astronomy PhD student at the University of Exeter. I pay for my PhD course fees and living expenses by working 3 days a week, and doing my study/research 3 days a week. This can make for a busy life but it is rewarding in the non-financial sense!
I did look at funded PhD places but there is lots of competition for them. My employer kindly agreed to let me go part-time so I could spend 2 days a week at university, on the understanding with the university that I would also spend a day of my weekends doing study/research.
Since then I have changed jobs and I now do a variety of jobs, mostly IT. This includes working part-time for the BAA doing a mix of office and IT work, so this isn’t pure astronomy work but it is interesting. To avoid any confusion, I also do some voluntary activities for the BAA, like managing the Photometry and Spectroscopy databases.
I am about to start demonstrating at university, another source of income which may be available to MSc/PhD students at other universities.
I have considered other sources of income which may be relevant to astronomy/physics graduates. There are websites which allow registered people to bid for small scale IT build work in different programming languages. It may be possible to find tutoring work in astronomy, physics or maths. I have also seen planetarium and astronomy educator roles come up at museums, and while these aren’t necessarily part-time it can be worth asking.
Good luck and let us know how you get on,
Andy