How to get the tenant out??

Possession - Section 8 and Section 21

I have a tenenat who owes me money from backpaid rent when he went into the local council and changed payments from me to him without my consent. the council did not advise me either by phone or in writing.
When i discovered the fact some time later I confronted the tenant and he promised to pay back the £1650 he owes me. This has not happened and i issues a section 21A notice giving him 2 months to leave which actually expired Friday night last.

Went to the property yesterday with managing agent to be verbally abused and threatened from tenant leaning out of u/s window. Have arranged to have Gas/Electric certs done for property on Monday - tenant has refused to allow access to them.
Reported incident to police who say it is a civil matter.

Previously had a complaint from next door to say tenant climbed over fence and did criminal damage to one of his trees and threatened his father who was working in garden at time.

As far as I know he has spoken to police about incident but am unsure outcome as he is abroad.

Will Section 8 cover this situation and how soon would it take to remove what is probably a "squatter" from my house?

Need advice urgently as reading some of the cases in the helpdesk / forum the law ould appear to be an ***

thanks

Peter