ECHR 1581
The European Court of Human Rights held in 2008 that UK holding DNA samples of individuals arrested but not convicted is unlawful. HMG has farted arround ever since with consultations etc.
Per wikipedia: According to The Independent on 27 July 2011, the UK government "has indicated that destroying the DNA of the innocent would be impossible because the records are mixed up in batches alongside the DNA of the guilty."
https://en.wikipedia.org/wiki/S_and_Marper_v_United_Kingdom
So UK government has essentially ignored the ECHR ruling.