Apologies for the previous long thread, any R&D part-timer could you please give some advices!

Also, does it happen to anyone that due to part-time work you have to extend your PhD to 4 years and beyond? How would you handle that? I think it'd be better to at least have some regular wages in the final stage, wouldn't it?

Or, is it BEST NOT to restart a PhD in this occasion?

Dear all,

I am currently working in the built environment sector with more than 6 years of experience.
In 2010 I was offered a 4-year fully funded PhD at a UK Doctoral Training Centre.
I completed the 1st part of the program which was an one-year MRes, then decided to defer due to some personal reasons (including not being happy with the assigned supervisor and the topic at that point). I have been back to the industry and working in a large international consultancy firm since 2011.

In the last 2 years, so many times I wanted to quit officially, but still couldn't make decision. I am originally from overseas and the chance I am holding used to be my dream 10 years ago. I might regret one day if I decline it. A PhD might open some doors in R&D if I stay in the UK, and valuable if I move back to my home country (or the region). But coming back to grad school after working for years (holding a decent paid job) is not an easy decision.

I am intending to switch to the R&D department within my firm and work for 1-2 days per week, in order to stay in touch with the industry (and promotion opportunity) and will use case studies from my company works for the PhD. The latest proposal is a practical engineering issue which is of the company's interest. My first supervisor comes from industrial background (he doesn't hold a PhD).

Does anyone have any experience in similar situations? How practical is the plan of working 1-2 days per week and full-time PhD in 2.5 years? Assumingly the last 6 months will be totally for writing up. I am 35 yo, single, having a mortgage (so income is an issue which is part of the reason why I want to have a steady part-time job). Any thought and advice would be much appreciated. Thanks a lot.