Hello,
A month ago, I sealed the deal on a PhD post that's sort of related to the research I wanted to do. I was happy, but unsure because of a number of reasons which I will explain, and this unsure-ness grew over time.

One of the main reasons is during my tour of the department, when I was shown the equipment and labs I would be working with, I was less than amazed, mainly because the department itself was quite small, and there was a clear prioritised research interest in the lab, which unfortunately was not the area I would be studying. Another reason is that simply the fact that while the project topic did relate to my research interests, it wasn't a direct link at all. Another reason is that I found out that I would be without my main supervisor for a good chunk of the first part of my PhD.

I have not yet started the PhD, nor recieved funding, due to not being formally enrolled yet.

Is it still possible for me to back out of this PhD at this stage and possibly pursue another PhD, or a research role?

Would this choice affect me quite negatively in my future prospects (I want to go into research)

Of course not. It should be fine. I recommend honesty with the supervisory team. They may even be able to make some changes if they know what it is you're not happy with. At any rate, at this stage they will probably be able to recycle your funding (give it to someone else) so they will not be at a loss if you do leave.

I think it is good to raise these issues before starting. It is much better than dropping out later because you aren't happy.

Good luck : )

Yep, you can back out any time.

If its a fully funded PhD, I'd follow the money and try to raise your concerns with the supervisory team to get things changed, as you might not get funding for your next application (I've been told that a lot of luck is needed for funding applications (quality of applicants for the year etc.).