RE: Moving from a rental property
I am also a landlord but have never withheld a deposit.
It is being made harder for landlords to do so nowadays.
However your landlord is a kn0b so to answer your question:
He may well live with the fact he is keeping your deposit and forget.
He could take you to a small claims court, you may get a county court judgment.
Or he might send the boys around.
I would ask him where you stand and tell him you will pay outstanding rent once you have handed back property.
If that dont work and he is obviously being a kn0b then maybe just do one!