Possession

Tenancy Types and Management

My tenant has not paid rent Apr 06, Nov 06 and Dec 06, she has paid May 06 to Oct 06 late every month.
She sent me a text 5 Dec telling me she was moving out in Jan 07.
I have relet the house from tomorrow and now she says I will have to go through the proper channels.
Apart from unpaid rent I now also have a young family with children homeless from tomorrow.
Please can you advise my best course of action and whether the text message is notice and what I can do about it.
Many thanks
Lisa