Original Tenant Never Left - Does their tenancy still stand?

Tenancy Types and Management

I have a situation where a tenant owing arrears moved her partner in and I was then told by the partner some months later when I was in the process of taking court action that she (the tenant)had left. Because of this I issued the partner a tenancy agreement. The new tenant accrued further arrears and I was successful in obtaining possession and a County Court Judgement.

At this time I discovered that the original tenant did not move out and had remained living there throughout the whole period. Am I right in believing that the original tenant is equally responsible for the rent arrears accrued from the time that I issued the partner a tenancy agreement? I have been told that as the original tenant did not surrender her tenancy and in fact never vacated (other than for a few weeks during a temporary seperation from her partner) her tenancy still stands.

I have further court proceedings against both parties and am looking to ask the court to uphold a judgement against the original tenant for the arrears accrued during the period when her partner informed me she had left. I have since learnt that both parties used their tenancy agreements to claim housing benefit whilst the other was working and that the local authority have investigated this matter to a successful conclusion.

I would be grateful for any advice any members can provide regarding this matter.