Tenant subletting entire flat

Access

My Tenant Mr X who took over a tenancy to my flat just over 4 months ago stopped paying rent 2 months ago and wasn't responding to emailscalls.

My agent entered the property based on an inspection and potential abandonment. Only to find Mr X had sublet the whole property. The people residing claimed they had been paying their rent to the Mr X and had a tenancy agreement. While my agent was there they phoned Mr X recording the conversation with Mr X. So my agent will potentially have
- Video evidence of more then one person residing at the property who is not Mr X
- Video conversation with illegal tenants talking to mr X about rent payments etc etc
- A tenancy agreement with Mr X and the unauthorised tenants