Can I eneforce them to leave before the first 6 months AST are up

Tenancy Types and Management

On July 15 I let AST to a couple with children. The property,Flat is above some shops. The children have been abusive and intimidating to other people in the area and damaged car windscreens. Although there is no proof in writing. The tenant was also storing a mini motor bike in the bedroom! There was also damage to common parts, steps leading up to the flat.Rent was being paid but not on standing order as agreed and they had to be prompted, also when I asked them to leave
, 23rd Sept, they stopped paying. On Sept 23 I gave notice to leave by the end of Nov, explaining all the complaints and the state of the flat. The local council say that they will not re-house them. Since I gave notice , Sept, no rent has been paid. It seems they also lied about how much the earn.
Can enforce them to leave before the 6 months is up?

Do I go for a warrent of possention now, or do I have to wait untill Jan 15 2007 when the agreement ends?
Either way they wont leave unless I enforce it.

Keith