For context, I am currently studying in one of the best universities in the UK and probably the best department for what I am studying.

I am about a year into my fully-funded PhD and am coming up to my yearly review, similar to a MPhil to PhD transfer exam.

For the last 6 months, I have felt an urge to quit for various reasons:

1) A sense of inadequacy and being in over my head. My project is very interdisciplinary, trying to incorporate ideas from other disciplines into my field. However, I am not acquainted with the other disciplines, nor is my supervisor, nor is anyone in the department. Also, I dont feel like I even have the requisite technical ability in my own field. I intially chose this topic because it was something i found intersting but never had the chance to study before, and that i could pick up the technical skills on the way. I feel like i overestimated my own abilties, the volume of literature to cover is overwhelming, and theres always something else I've missed when I'm forming my research questions. Disappointingly, theres no one to tell me so and I often find myself finding out later when an article pops up. I am so fearful that what i am doing, may not be unique enough without me knowing, after I dedicate so much effort to it. On top of it all, i don't really love my topic either. I find it okay.

2) Before starting, I had the usual scenes of smiles, respect and reverence play out in my head as i proudly sit with my PhD. I also wanted to be a researcher in the future and eventually a lecturer. Being in the environment, i no longer care for that dream and can't imagine spending the rest of my life in academia. It just seems dull, constantly stressful and uninteresting. I feel like there are other jobs, I'd be much happier in and that are more lucrative. This in turn has made me lethargic, disinterested in my work, and depressed. I feel like everything im doing is pointless and all for show.

3) I have done an extensive literature review and come up with a plan for the work, which sounds reasonable. However, I have a feeling deep down, that my questions are useless and too abstract. Like im trying to be too clever and sophisticated. Furthermore, I have suggested that i am going to do some complicated modelling, which I currently dont have the abilities nor skills for, and am so afraid that I wont be able to do it.

I'm hesitant to leave because of all the effort I've already put in, and the reality that the work will be just be discarded. I've got a good job lined up for the autumn (not the best i feel like i could secure but good, as I applied when all schemes were full) should I quit, so i wont be out doing nothing. I've contemplated remaining on to obtain an MPhil as it may prove useful in securing other prestiguous jobs in the future, but i would have to dedicate another year to this because i havent done any actual data collection as of now. I feel like dedicating another year which will undoubtedly be mighty stressful, will just leave me further unfulfilled and am unsure whether the extra time to possibly securing an MPhil will be even worth it. For context, I am hoping to go into a consulting career.

Any advice, welcome

I'm probably not the best person to offer advice but to me it sounds like you've already made up your mind. If the thought of dedicating another year to it for an MPhil fills you with dread then another 2-3 yrs to obtain a PhD that you have already lost interest in would be hell.

I still have an interest in my topic and I'm on the verge of sacking it after so long.

The main thing I want to say is are you sure this is not just a more extreme form of impostor syndrome?

Maybe you're right. I've never personally felt inferior, although i studied at the same institute at the Masters level. I've spoken to other PhD students, and they dont seem to have the same issues as me, but that is just a few people.

Regardless, another factor that's really playing on my mind is that I can no longer see an end goal. Initially, i imagined a career in academia, but now i dont want to walk that path. I'm struggling to see a result of the PhD, that will take me somewhere that i could not have reached without it.

I feel very similar, having no goal ahead and all the uncertainty that comes with it... I am trying to finish my phd, it is fully funded but then the question is if i were to quit, would i have to return all that money? I am trying to continue, telling myself it is just a little bit more here and a little bit more there but it generally feels like continuing the phd is equal to voluntarily putting myself into a virtual with no clear benefit of doing so. I hope you will find a way that suits you. I suppose in this kind of situation it is only you who has the right to make the decision. The thing is that there is no right or wrong decision. Yes, you've put up work into it but if you don't see that there is anything useful for you personally coming from it then you shouldn't dwell on what you've done but rather on what you want to do from this moment on.

You are still early in your candidature, only about a year in and for half the duration you wanted to quit. No offence, I think you may find the PhD years ahead difficult to go through. You also said that you got a good job lined up for the autumn. Would you consider taking a break, going for that job, and then using that time to think if you still want that PhD?

Everything you write suggests that you should take the job. Research and academia are not for everyone and there's no disgrace in accepting that and walking away to something you think offers more of what you want out of life. I suspect that once you're out of the environment, your regrets will subside as you'll be busy with something else. At another stage in life you may feel differently and want another go but for now I'd quit if I were you.

Knowing when to quit is an important skill.
Maybe the timing is wrong for you, You can always try again later in life.

I'm in a very similar situation. my area is also interdisciplinary, which initially sounded really exciting, but now I've come to realise it just means you're bouncing around different departments with no one supervisor who understands what my PhD is about. it's really getting me down, but because I've taken some breaks since my undergraduate degree plus some jobs abroad, I get comments from friends and family like "welcome to the real world of job stress" which is pretty patronising.

I remember the time when I wanted to quit my PhD too. I had a supervisor I hated, I felt like my research was going nowhere and I stated losing my hair due to extreme stress. What stopped me from quitting was the fact that this was MY research, not my supervisor's. So I went back and grabbed the bull by both horns, got rid of the troublesome supervisor and found a better one kept my head down and tail up for the next 3 years, wrote like crazy ( and it did make me!). I submitted my 4th and final draft for examination a month ago.

From what you've shared, I can't think of a single reason to continue. I mean, the main thing is do you WANT to continue? The only incentive for continuing I can find in what you have said is...

I agree with pm and TQ. I personally did not have the courage to quit and ended up spending 5 years without PhD at the end.
Quitting now is better than tomorrow. The early you do it, the less you have to explain to prospective employers.
I tell myself, if I have even quitted after 3 years, it would have been better than 5 year.