If your fixed term AST comes to an end on 18 February 2013, you can move out on or before this date and the contract you have with your landlord comes to an end. You do not need to give your landlord notice to this effect, but it would be prudent to let them know that you intend moving out at the end of the contractual period. They may need to arrange an inventory clerk and check out process. This will speed up the return of your deposit and let your landlord know that he has to start the process of repaying it.
Originally Posted by kerad84
If you remain in the property, even for a day beyond the last day, a periodic tenancy is automatically created and you would have to continue paying rent, give one months notice, or move out on the date specified in the Sec21.
I offer my advice freely, but I am not an expert, solicitor or judge. It is simply my experience of being a landlord and what I have learnt along the way. I make no warranty for my opinion.