You need to be careful to avoid being accused of 'harassment'. For example, a Sheffield newsagent got fed up of all the people who never paid their paper bills, so he put big notices in his window saying things like "Arthur Price of 43 Cunningham Gardens owes this shop £87.70". He received a visit from the police who advised him that he was committing a criminal offence under Section 40 of the Administration of Justice Act, under which it is illegal to subject a debtor (or members of his family or household) to alarm, distress or humiliation.
The Protection from Harassment Act 1997 also makes it an offence to cause harassment, alarm or distress to another person (irrespective of whether any debt is involved) in either verbal or written form. However such actions only become illegal if they occur on two or more occasions.
Despite the foregoing it remains perfectly legal to simply state the truth about someone. If it wasn't, the tabloid newspapers would soon go out of business.
Chris