[DanBC]

England has an extensive DNA database (largest in the world) and it's hard to get taken off it, even if you voluntarily give your DNA. http://news.bbc.co.uk/2/hi/uk_news/7532856.stm

> Innocent people who volunteer to give a DNA sample during a police inquiry, for instance to help narrow a police search in a major murder investigation, also have their details kept on record.

Most people don't volunteer their DNA; it's taken off them when they're arrested, and it's kept even if they're not convicted. It's even kept if they're released without charge, although there are time limits for that after a 2008 case. http://news.bbc.co.uk/2/hi/uk/7764069.stm