End of tenancy deposit retention

Tenancy Deposits

My tenant has moved out but left the house filthy, garden very overgrown, stains on carpets. Flat roof has been leaking a while and hes not informed the letting agent. Hes painted a room a different colour and got the it everywhere.

Letting agent says they will get in a cleaner and decorator and deduct from depoit But i would like to clean it myself and get im my own gardener etc. Are there any rules as to if i can do this or not and how much i can deduct from his deposit for this if i do certain works myself? I cant see anything on his contract about this, it does state how he should leave the though and he hasnt adhered to that.

Thanks