How much is your deposit? Usually I don't pay the last month, so the owner has one month of deposit. This reduces the losses. If the owner has 40,000 of your money, do you really want to pay a lawyer 10,000, to try to get back 20,000? It doesn't make much sense. Try to do a good case for the small claim tribunal because it's free, but don't pay money to try to get back some money.
Also, the damage seems at the borderline of normal 'wear and tear'. How long did you spend in the flat? If you spent one year, I think it's borderline. If you spent 5 years I have no doubt the landlord needs to return you the money.