Once you have been discharged from your Trust Deed, you are officially debt free, and this should be reflected in your credit score within 3 months of completion.
If your debts are not shown as being satisfied within this time, you should contact your creditors and request them to update your credit file. Once this has been done, you can begin rebuilding your credit. How long it will take for your credit file to be updated can vary. If you do something about your credit rating the sooner, the better.