MRes degrees are pretty rare in humanities and I'd be surprised to see many places asking for them specifically. What is more common is to require an MA degree with a significant research component, which usually means a taught course with a research based dissertation required at the end for completion.
However, the amount of funding available for research varies hugely from year to year so I would not tie myself too much to a specific university / department. I'm currently doing a fully funded PhD in English (after doing just an MA which required dissertation), from my experiences applying and from what I know from others, if you want to get funding for a PhD you have to be strategic about what you apply for and be willing to change your plans if Oxbridge doesn't work out. One of my friends was really set on going to Oxford for his PhD. He applied after completing their MA but didn't get in so he did a second MA (in a different but related discipline), started corresponding with a prospective supervisor at Oxford and through them even managed to get an internship working as a research assistant on a larger projects. He was more than qualified and did everything right but after all of that they still didn't offer him funding. UCL did so he went there and is now very happy. I have a feeling he would have even been able to get funding somewhere else before the 2nd MA if he had looked at other options.