I was in a similar situation as you a few years ago. I have written a few answers on this SE on the topic:
In the end, this depends on many factors, including your nationality, your field, and your institution. Funding for a PhD for a non-British and non-European person is rare, because it is the financial equivalent of 3 or so British students. You will be responsible for International Student tuition (at my old university this was about 17k£/year plus living expenses, all of which you need to have the first year prepared for in order to get your visa.
So we need more information, and your first point of enquiry should be the supervisor who wants to work with you.
To be quite honest, even with stellar grades, this would be extremely difficult unless you're very lucky. I had several PhD offers in the UK but in the end I gave up and went to Europe, and didn't look back. I would advise you consider doing a PhD in the EU - in many cases these are fully funded, with no discrimination based on nationality.
But: maybe there is something your prospective supervisor knows about. Maybe there are nationality-based scholarships. Maybe there are scholarships from your home country. The only way to know is to ask your supervisor, the International Office, and google. The remaining scholarships are very competitive (e.g. Fullbright) but worth a shot as well.