hi,
i presume you already checked what your university/department has to offer.
you won't be lucky with the research councils unless you have lived in Britain for the three years prior to starting your PhD.
if you are in london, you could check the university of london websites.
apart from that, you should probably be looking for funding opportunities from your home country (f.e. from the government).
you can also check out subject-specific funding opportunities, for example the wenner gren if you are doing anthropological fieldwork.
if you are a woman, check out the IFUW plus their national sections, they tend to prefer students who aren't in their first year.
if you have specific circumstances (for example you come from a marginal region, you are a minority of some kind, you are re-entering academia after quitting for having a child...) there might be charities around targetting just this.