Tenant Rescinds Notice

Tenancy Types and Management

Hi,
We have a tenant who approx 6 weeks ago gave notice to end their tenancy at the end of the initial six months which is 25/10/13. One of our other tenants has viewed the property and wants to swap from their one bed flat to this 2 bed property and we have agreed in principle although not produced any paperwork yet.

The existing tenant has now sent us a letter rescinding their notice. We want to ensure the tenant does actually leave as we want the second tenant to be able to carry out the swap we promised. I have two questions:

1. I understand the tenants notice would normally end the tenancy but am I obliged to accept the retraction of notice?

2. If I am not obliged to accept the retraction, and they do not leave, what is my next step for possession, do I go straight to court for possession?