@Bainesy1969 has a thought-provoking blog entry on the retention of DNA samples vs. DNA profiles in the UK and what EU law requires. He begins:
On 26 July 2011 The Telegraph reported that “Innocent people’s DNA profiles won’t be deleted after all, minister admits”. It said that
“police will retain DNA profiles in anonymised form, leaving open the possibility of connecting them up with people’s names, ministers have admitted”.
In S and Marper v United Kingdom  ECHR 1581 the European Court of Human Rights held that indefinite retention by the police of fingerprints and DNA samples of two people who had been arrested but not convicted of criminal offences was a breach of their rights under Article 8 of the European Convention on Human Rights (overturning a decision upheld at each instance in the English courts).
The Protection of Freedoms Bill proposes, accordingly, to amend the Police and Criminal Evidence Act 1984 (“PACE”) so that – broadly – a lawfully taken DNA sample (and fingerprints) must be destroyed after three (or in some cases five) years if the suspect has not been convicted of an offence to which the sample relates
Read more on Information Rights and Wrongs.