Rent Arrears and repossesion

Rent Arrears

We have a tenant who began his tenancy on July 5th 08. (We use RLA tenancy agreements). He occupies a room in our HMO and rent includes all bills. We didn't do anything at the end of his fixed term and so have a periodic agreement.

Until he lost his job in Jan he always paid, though rarely on time, but has since fallen into arrears. We have tried to give him chances to pay and have been given nothing but false promises.

Firstly does the section 21 within the terms expire on the day the fixed term expires or does it still stand? The Section 21 notice originally served states this notice expires AFTER 04 Jan 09 but the text prior says that I require possession AFTER the expiry of this notice.

Today he is 8 weeks and 1 day in arrears. I'm not sure if we can write to him asking him to leave in 2 weeks or if more notice is required? The RLA website says that before a section 8 notice is served the relevant valid notice period needs to have been served. What is this?