Deed of Surrender

Tenancy Types and Management

I need to end a tenancy before the end of the term due to a couple having a relationship breakdown. One of them wants to remain in the property under a new tenancy. We have agreed to sign a Deed of Surrender, but when should the new tenancy start? If it is dated after the Deed of Surrender the property will be occupied without a tenancy in force and if it is before the Deed signing then there will be two tenancies in operation. To sign both deed and new tenancy on the same day seems difficult administratively. What if the deed is signed and then the tenant refuses to sign the new tenancy and effectively becomes a squatter?? Many thanks, Ivor Letafew.