I am a senior undergraduate at a UK uni.
Funding for international students in the UK is definitely NOT guaranteed, and is very competitive. My uni does not fund a single international physics phd student (although there are other sources of funding here). At Cambridge/Oxford there are a lot more scholarships than other unis for international students, but in most cases you have to apply to the scholarship separately. In Scotland the main scholarship is SUPA
. Other than that, you have to look for scholarships at the institutions you are interested in separately to see what you may be eligible for.