Council Tax debt is an unsecured debt which means that it will expire after 6 years according to the Limitation Act 1980. However, it is unlikely that someone in Council Tax arrears will be able to wait that long as the Council will usually ask for a liability order if the 7 day payment reminders are ignored. A liability order is granted by a magistrate and enables the council to collect the unpaid Council Tax from wages and some benefits.
If there is no other way to recover the Council Tax debt, the Council can send Bailiffs to seize the property of the person in arrears. Finally the council can take the matter to court. The court will then decide if the person in arrears has a valid reason for not paying their Council Tax or not.