Letting agent gone into liquidation

Hello all,

I'm a private landlord who has been letting out my flat through a letting agent. Recently, my first tenants moved out and the letting agent moved in a new tenant without consulting me and hence without my consent. I've not been paid any rent from the agent since january and have now been informed by the letting agent that they have gone into liquidation.Needless to say I am very concerned and have several questions:

1. Am I liable for any deposit the new tenant paid to the letting agent? Bearing in mind I never signed, nor agreed to her moving in. I do not think the deposit was registered with an external body.
2. Is there any chance of recovering the owed rent?
3. Where do I stand if this new tenant is problematic?

It looks like the letting agent has cut and run, leaving me seriously out of pocket and with a tenant I know nothing about. I'm not a professional landlord, just someone who moved out of the area and is still paying the mortgage and costs on it. I have the contact details for the new tenant, but have so far been unable to speak to them. If anyone could give me guidance or advice on what I can/should do, that would be hugely appreciated.

Thanks.