I have been offered a place at a good uni to start a PhD but have been unable to secure funding. I am able to pay the tuition fees and my job would cover any other expenses with me working approx. 20-24 hours a week, but there is an obvious issue with time constraints.

The process would not be too unfamiliar for me, as this is what I did during my MA at the same Uni, the only difference is that I chose to do my MA part-time. I would not be willing to do the same for the PhD as I think 6 years is too long.

My wife is supportive of the idea (to some extent), and I am committed to the idea as I would like to take up a career in academia. However, I appreciate that doing a full-time PhD requires a lot of work, and I would like to get some advice on what others would think about the additional part-time work? Has anyone done this themselves?

Do you have a clear sense of why you didn't get funding and is it something that you could fix? If so it might be worth self-funding a first year part-time to work intensively on the proposal with your supervisor and reapply for funding.
If not, then get someone to talk honestly to you about what the academic job market in philosophy is like and what you'd need in terms of publications, teaching experience, areas of expertise etc to be in with a chance. You need to be very aware of how tough it is before you self-fund. (Ask them to be brutally honest about the job itself too - it's not as nice as many people think it is.) The snag in your plan is that if you work that many hours in another job, you are probably not going to have time to acquire the sort of cv that would be competitive, even if you managed to finish the thesis in 3 or more probably 4 years, particularly if you intend to spend any time with your wife. Trying to go fulltime with those work commitments could in fact be an error on that front. Finally, I'd ask yourself how much you'd (and your wife) resent the fees and years of lost fulltime earnings if (as is the case with most PhD students) you did not get an academic job. Sadly a PhD in Philosophy is not likely to add much to your value on the non-academic job market, so this is really something you have to both be fully on board with. If you still can't imagine anything other than a PhD and a try at the academic job market making you happy, then go for it, but if you have doubts then I wouldn't self-fund.

The lacklustre CV is certainly a worry of mine, and I appreciate what you say about the amount of time spent in another job putting me at a significant disadvantage to other candidates. That said, I am not scared of hard work if this is all that is required - my worry is that even my best may not be enough.

I am good friends with my undergraduate professor, so will certainly take your advice and ask him to be honest about academia - he certainly won't have a problem saying it as it is.

As for funding, I certainly aim to reapply, and it is not that I did not secure funding having tried (unfortunately due to an issue with my application being accepted before the deadline, I was never put forward for it). That said I am doubtful of acquiring funding from the AHRC anyway - not to be pessimistic.

Thanks for the advice.

The problem for the CV and a time consuming additional job is that you are likely to struggle to be able to find the right times to help organise conferences, attend vital workshops, get teaching experience etc. These things are essential to a good CV for employment afterwards but tend to be at fixed times that you may struggle to work around your job.

I would strongly recommend that you reconsider studying part time. This need not take the full 6 years. 5 years is very feasible, and compares well to many full timers who overrun the 3 years routinely and often take 4 years.

Don't rule out AHRC too readily. I self funded my first year, and applied to AHRC during that, and won funding for the rest of my PhD. I was a part time student for disability/health reasons, but they still funded me.