In 2004 the UK government changed the law on DNA collection, and retention, to allow the police to take DNA from people who have not been charged, i.e. innocent poeople
Following this there was a test case, brough by two individuals, “S” and “Marper”, resulting in a case that went all the way to the ECHR, and resulted in a verdict against the UK Government in Decemebr 2008.
Following this there was an expectation by many that the UK government would delete innocents people data from the data base. Though this site, bucked the trend and suggested that the police would not delete DNA from innocent people.
Despite comments by the Home Secretary, repeated in answer to questions in the House of Commons, that they would follow the ruling of the ECHR, this is not really the case.
The government does intend to retain data of innocent people, they have just put a time limit on it. It is 12 years if your accused of a violent of sex crime, and the emphaiss here is on accused, rather than charged, convicted, or there been any evidence against you at all. If its a lesser crime it wil be 6 years.
Though in 6 years time the governmetn could change the law again, or they could just chose to not delete the data.
The net result is if your arrested, regardless of the circumstances, your DNA will be taken and kept.