Part-time PhD – good idea?

Too many variables to generalize. Saying you want to be an academic is one thing - are you aiming for the top of academia? Because tenured professors almost invariably have a PhD or are obviously exceptional talents in their field with general acknowledgement from other experts about the quality of their publications being at PhD level or above. A lot of lecturers and senior lecturers might only have masters degrees (one or more). Then you throw in other variables like whether work is going to be full/part time and whether you have a family to raise already? Personal circumstances? It all depends 😀

This isn't accurate at all really as far as I am aware?

To be a lecturer in the UK you realistically need a PhD now. It would be very unusual in most fields to only have a masters these days - outside of teaching only positions in e.g. languages, or perhaps in creative/performing arts areas if they are teaching the "production" side rather than theory side of things. For most general academic fields at a uni in the UK a PhD would be the standard expectation I believe. The exception would be current PhD students contributing to teaching, which isn't uncommon.

Also tenure doesn't exist really in the UK to my knowledge. There are permanent academic positions (e.g. permanent chairs/professorships etc) but these are very rare and it's more typical I think for academics to work on rolling fixed term contracts and often having to move to follow when its not picked up.

Nah I still know a fair few lecturers who only have masters. I am not aware of the very latest appointments but certainly from my classmates 20 years ago that was the case.

When I say tenured I mean for life as in permanent. Again I am not up to date with what is happening now but I know there was "competition" amongst my year as to who would make first prof for life.