The subtenancy will be valid for as long as the mesne tenancy continues. But whether the subtenant has any rights after the mesne tenancy ends depends on whether the subtenancy is legal or not.
This depends on:
- what type of tenancy the mesne landlord has
- what it says in the mesne landlord’s tenancy agreement
- whether the head landlord agreed to the subtenancy.
If the head landlord knowingly accepts rent directly from the subtenant, it may become legal. This is true even if the subtenancy was originally illegal (for example, if the mesne landlord’s tenancy agreement said subletting is not allowed). By accepting rent, the head landlord may be admitting that the subtenant has a right to live in the property. However, some landlords will get round this by saying that they are only accepting the money as something called a ‘charge for use and occupation’ and not as rent. This is a complicated area of law, so get advice.
If your landlord’s tenancy ends and your subtenancy remains illegal, it is worth trying to negotiate with the head landlord, but s/he can evict you very easily.