@AC: REAL reason for keeping the data
Actually you can find out about jewish, black or whatever ancestry using DNA samples for a couple of years now. According to the guys who run www.rootsforreal.com you need high resolution mtDNA sampling and specific Y-DNA markers and a huge geographic dna database to do this. Apparently this technique is already being used in the forensic sciences. The "DNA fingerprint" (autosomal DNA) used in court for identifying parentage or murderers is only suitable for detecting recent ancestry up to the grandfather generation, if you're lucky. According to wiki the UK National DNA Database only stores the "DNA fingerprint", so you're safe for now Mr Cohen or is it Yoruba?