I don't know anything about your subject area and how easy it would be to switch fields, I think it very much depends on potential supervisors and how you compare to the other people you are competing with for a position, (and your project proposal if you have to write your own, rather than work on a pre-defined project).
As regards funding, I believe it very much depends on whthe funding source, as to who is eligable for it, some types of funding require you to be from the UK, others from within the EU, others have no restrictions, again this is something that you would have to check with potential departments or supervisors.