Getting deposit from DPS for damage?

Tenancy Deposits

I didn%E2%80%99t do an inventory (a huge mistake I now know) I have pictures & videos of the room how it was left and very poor/basic photos of before? The deposit is %C2£300 but to give you an idea of how bad the room was left, I%E2%80%99ve had to remove everything from the room including underlay as every bodily fluid was dispensed all over the floor. He set fire to the mattress.

The tenant left a huge rent arrears bill, which I won at small claims. I know I can apply and get the deposit that way. But I don%E2%80%99t want to reduce his arrears, if I have any hope in getting the deposit for the damages?

Any advice would be welcome