Tenants behind on rent - what contracts

Rent Arrears

We have had the same tenants in a property for about 4 years. They have always been bad payers, but have kept paying - albeit with chasing.

We raised a Section 8 as amended by Section 151 of the Housing Act 1996 document for the back rent of £1120 during the period 2/8/08 to 11/10/08. The tenant is still behind in their rent by over £1200 and the delays of payment are getting longer, with smaller amounts paid each time.

I give them a rental statement monthly but its posted - not delivered, so unsigned.

I issued the document to the address - but again, it wasn't signed as being received.

I am worried on 4 counts:-

1) How can I ensure this doesn't turn into a sitting tenant. The Section 8 is the only thing in force now between us and that is unsigned by them.
2) How quickly could we get them out if need be.?
3) How can we put pressure on him to catch up on his payments?
4) Should I get him to sign for his rent each week and sign the Section 8 or any other document that he's received it? (Sounds daft now looking back on this)?