None. The purpose of the National DNA Database (NDNAD) is to hold a record of a person’s DNA which can be matched against DNA taken from crime scenes. If there is a match the police are notified and make further inquiries. The NDNAD holds the person’s name, date of birth, ethnic appearance, gender, a link to any record on the police national computer, and information about the police force which took the sample. This is sufficient for the police to be able to contact the person if required. It is not necessary for the NDNAD itself to hold the person’s postal address.
The address someone is living at when a DNA sample is taken from them will of course become outdated when they move, so adding this address would impose extra work on the police for the sake of information which in many cases would soon become out of date. In order to keep address information accurate, it would be necessary to monitor changes of address of the 4 million people on the database. This would be expensive and intrusive without adding anything useful to police operations.