Right people will tend to get funding for 3 years and then self-fund year 4. Can this be done in reverse?

yaaa

I take it you mean to successfully apply for a funded place, and then defer funding for a year, is that right? As opposed to registering for a fill-time PhD on a self-funding basis then applying at the start of the second year to continue what you've started?

Tha latter is risky as your application might not be successful. With regard to the former - I very much doubt it. Most university departments are allocated funding on the basis of recruiting PhD students within a specified financial year. Funding allocation decisions are made at high uni levels, and I very much doubt that they would allow this just for an individual preference.(continues....)

I can [sort of] see the logic behind your question - most people DO go into a 4th year. However stop and think about what the first year involves: making and developing new contacts, lit review, first experiments, maybe beginning to prepare for conferences. You’ve also got the added factor of MPhil to PhD transfer assessment at the end of the 1st year.

With all this going on, self funding, especially if you were holding down a job to do this, would be quite stressful. You may also miss important seminars/meetings because you might have to work. When you're in the 4th year, you're just writing up (incidentally, I don't mean the word "just" to trivialise the writing-up process! I mean that it's the only PhD related thing you're doing, as opposed to all the activities in your first year.) It's a lot easier to self-fund when your PhD activities are more streamlined into writing, rather than a lot of other things.