In reply to Alan James - Rockfax:
Depending on the sum owed it may be worth writing it off, but if it is a substantial sum then still persue.
My other half used to work for a collection agency with difficult debtors, her company bought the debt from the creditor. A lot of these people never paid up and the debt was then sold on to another company and so on.
If it is a company who is still trading you stand a better chance of recovering with your CCJ aginst them if they want to get any credit. If they still refuse to pay up then you can obtain a winding up order(or threaten them with one), This last option usually works a treat.
HTH