Seeking possesion without a current AST

Tenancy Types and Management

I rented a flat to a couple for three years without a problem, then I was informed that the tenants had decided to split up. I was concerned as the tenant who moved on was the one who handled all the affairs efficiently and as the tenancy had just expired (Sept 2006) I was reluctant to issue a new AST, also the tenant indicated they intended to make a clean start elsewhere. This seemed a good option for all concerned, but that was back in September 2006. Whenever i enquired to tenant about them leaving they suggested that they are looking but cant find anything suitable, the rent was being paid so i was willing to wait and wasn’t too concerned. Then two months ago they stopped paying the rent and further suggested that i had opened their mail and had spoke to other tenants about them things were clearly deteriorating. and one l the current tenancy expired in September last year I want to gain possession quickly, What is quickest option?.........Concerned Landlord