Deposit and rent arrears?

This is related to another thread I posted recently, but the subject is different:

I'm in the process of enforcing an eviction order granted by the court for rent arrears. I then intend to pursue the tenant for the debt through the courts. There is a deposit in place that equates to half of the current arrears.

My question: in order to release the deposit (to me, against unpaid rent) do I need a court judgment, simple proof of the balance via the agent's ledger balance perhaps, or some other specific proof?

And would it be usual to start debt recovery procedings prior to 'drawdown' of deposit, or after this has taken place?

Thanks.