I'm a recent graduate who is considering pursuing a Ph.D. within 18 months - 2.5 years' time. I've been in a graduate job as an engineer for 6 months that is related to my master's degree (in the Energy sector), however, I'm not enjoying a 9-5 corporate role and I know it isn't for me.

My scheme finishes in 18 months, and I then plan to take a sabbatical year out, during which I am considering applying for funded PhDs. My Master's degree was in Renewable Energy Engineering, which I achieved a distinction in (it wasn't from a Russel Group university, but still a well-respected one). However, my undergraduate degree was in Physics (at a world-leading university), which I unfortunately only received a 2.2 in. I was very young (only 20) when I graduated, and I'm hoping that having a distinction in the topic I'd be aiming for a Ph.D. in (research into renewable energy) would help me. I also plan to finish my graduate scheme despite not enjoying it, so I'd have two years of industry experience. I'd be hoping to start a Ph.D. in Autumn 2023, and I'll still only be 24 then.

I guess my question is do I even stand a chance of getting funding with my 2.2? I'm hoping my distinction and industry experience could redeem me, as I would be unable to entertain doing a self-funded PhD (unless I can get an industry sponsor). I miss learning new things, and challenging myself, and pursuing my curiosity for the sake of it, and am willing to take a significant pay cut to get a chance to experience that at university again as a PhD student. Staring at spreadsheets and doing busy-work 9-5 isn't cutting it for me.

Of course you do. I recently interview candidates for PhD with my old boss. the two that were chosen had 2.2- but had industry experience and a passion for the area. You could see they taught about why they wanted a PhD and what they were interested in studying.
Start by reaching out to PI-one who interested align with yours- send each and individual email ( don't mass email the same letter to all)- ask do they have funds or would they be willing to help you apply for funding. Try have an idea of what funding you might be eligible to apply for and areas your interesting in studying.

I had a 2:2 and a Masters degree. So do tons of people. Most people in academia with a Masters degree also got a 2:2! The most important thing is passion for your subject.

By the way, I've learned that biographical details sometimes annoy people. For example I also started my undergraduate degree really young and kind of struggled more than I might've done otherwise. I always assumed people would be compassionate and supportive, but whilst one or two people were, the majority of people hadn't had that experience and were just either confused or annoyed at me for bringing it up. They thought I was bragging about how smart I was, and nobody succeeds in academia just because they're smart. In fact if anything I spent a lot of time in the beginning having to fight off my "greater than / less than" fears at having gone to Uni so young and achieved a lot and yet also not having a string of perfect grades and feeling kinda inadequate. I had to learn that none of those things mattered to anyone, which was pretty annoying because they'd had a really big impact on my life. But what it did do was give me a bunch of personal strengths and understandings that I very much drew heavily on later -- even the best PhDs can get very stressful. So just don't worry about any supposed weaknesses you imagine you might have, because from an academic perspective you'll look awesome (I used to work with people in various sustainability / renewables roles and it seems a ton of people have no relevant masters AND no physics background AND no industry experience, so just think how great you'll look for having all three). I hope you find things to enjoy from the rest of your training which might open up new doors for you in the future. There can be something nice about knowing you're not going to do something long-term in a way which kind of takes the pressure off a bit to just enjoy it for what it is, I think...

Absolutely!
Although it will be much tougher without a First, because you will be competing against those people that did (although obviously grades are not the whole story). Coming from a humanities background I can say that funded PhD positions are extremely competitive, lots of people apply, and lots of people inevitably lose out. This had been my experience, because although I did have good marks (First undergrad and 2:1 masters), there were many other people out there with better grades, better connections to relevant academics, and/or (initially at least) better practical/industry experience. Following my Masters I was trying to get on funded programmes (with the PhD questions already developed by academics) for about 5 years. I would apply to one or two per year whilst working full time, dedicating a ton of time researching and writing proposals. I got interviews to about half of all those I applied for, but was always unsuccessful. In the end I was successful and managed to get on an industry funded PhD. I think I was successful here because I developed my own research idea instead of trying to fit into an existing programme, and because I developed a good set of contacts in industry and academia.
This approach worked for me because: 1) my grades were slightly weaker than they would be for other candidates, 2) it had been several years since my Masters so I would not have the opportunity of being 'shepherded' or guided into a programme, and 3) because my practical/industry background and my relationships with industry professionals had grown to be much stronger than my connections to universities and academics.
I don't know how it works with engineering, but I think its completely possible for you to do it. You just need to keep the faith and be resilient because it may take a while. Get a good research idea, and build up relationships and connections. Good luck!