Many student landlords ask for a UK-based guarantor who agrees to cover your rent if you do not pay. If you do not have one, you still have several options.

Pay rent in advanceSome landlords will accept several months, or occasionally the full tenancy, upfront instead of a guarantor.
Use a guarantor serviceCompanies such as Housing Hand act as a commercial guarantor in return for a fee. Check the total cost and terms carefully before signing up.
Ask your universitySome universities run guarantor schemes or can direct international and estranged students towards landlords with more flexible requirements.
Look for purpose-built student accommodationLarger student accommodation providers are sometimes more flexible than individual private landlords and may accept alternative financial checks.
Provide other evidenceA landlord may accept proof of savings, regular income, scholarship funding or parental support from overseas, although they are not required to.

Before paying any large amount upfront, make sure you have signed the tenancy agreement, verified the landlord or agent, and confirmed exactly what the payment covers.

If one landlord refuses to proceed without a UK guarantor, do not assume every property will be the same. Requirements vary considerably between landlords and letting agents.