UC Housing Costs when the named tenant has left

Could someone point me in the direction of the UC regs that support this from the Shelter website please?

https://england.shelter.org.uk/professional_resources/news_and_updates/universal_credit_after_a_joint_tenant_or_partner_leaves

When the claimant is not liable to pay rent
Some claimants are not liable to pay rent. For example, a person not on the tenancy agreement living with their partner.

Claimants in this situation can qualify for housing cost payments if they are treated as liable under the universal credit regulations. This means they can receive help with housing costs where the person liable for rent is not making payments.

When the person liable to pay rent leaves
A claimant is eligible for the housing costs element if:

the person liable to make payments is not doing so

the claimant has to make payments to remain in the accommodation

it is unreasonable to expect the claimant to make other arrangements

it is reasonable to treat the claimant as liable to make the payments

This can help someone keep accommodation. For example, where a sole tenant has left and their partner needs to keep up with rent so they can remain in the property. A landlord might start eviction proceedings if arrears accrue.

This rule is not limited to cases of relationship breakdown. For example, if a sole tenant is sent to prison, another adult in the household could be treated as liable.

https://www.legislation.gov.uk/uksi/2013/376/schedule/2

UC reg s
25 (3) ii   and   Schedule 2, part 1 of those regs cover who is treated as liable