Tenant Status After Death of Original Tenant

Please could you determine if my tenant is now considered an unauthorised occupant:

The original tenancy agreement was taken out in 2015 by his father, who died two years ago, and the tenant has been paying the rent ever since.

These payments have become irregular, and I now require the property back as I want to sell it.

View Related Handbook Page

Succession Rights and Rights of Survivorship

If a joint tenant dies, the remaining joint tenant(s) are entitled to remain in the property (having a right of survivorship). They become liable for the rent.