It's a funny thing, PhD funding. It's nothing like the funding for undergraduate study. Sometimes the best candidates don't even get funding. And if you do secure three years of funding, the harsh reality is that it probably won't be enough to live on. Add to that the fact that many PhD research projects won't be completed on time, and there are many postgraduate students at British Universities in severe financial hardship.
Some supervisors are particularly cynical about student funding. Instead of working towards a 'get out' plan, students are deliberately held back, to complete research, analysis or manuscripts. A PhD project is not the student's life work. It is a stepping stone to their future. And that future cannot begin until the thesis is handed in and the viva voce exam completed.
A peculiar trap is the 'continuing' status. No funding is available. Technically, lab work must have been completed. Students must be in the final stages of analysis and thesis preparation. The rules are stretched, however, to accommodate the never-ending search for the perfect result.
Scientists, the perfect result doesn't exist. If it did, we wouldn't need research. We could simply set the hypothesis and only do experiments to prove it is true. More important is the research which seeks to explain the imperfect. Sometimes, the answer is bigger than a PhD project, and students and supervisors would do well to remember this.
The PhD thesis should set the hypothesis and the means by which this hypothesis will be tested. Once those tests have been done, the hypothesis will have been proved or not. That is the thesis. A thorough examination of the literature will aid the student in the discussion of the thesis. A well written thesis, with sound arguments based on a solid understanding of the context of the work will secure the award of PhD.
It's not rocket science. Don't make it more complicated that it needs to be. And above all, the PhD student knows more about the minutia of their field than the supervisor. Be confident, and enjoy your PhD.