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IN THE US, it would be protected by steel doors and armed guards. In Britain,
anonymity does the job. Tucked away on an industrial estate near Birmingham,
you’d scarcely know the brick-and-glass building was there—let alone that
it houses the biggest collection of human DNA in the world. A collection that’s
getting bigger—and more contentious—by the day.

For years, police in Britain have been quietly exercising their right to
collect saliva swabs from almost anyone they take into custody. Those swabs now
fill scores of industrial freezers in the basement of the anonymous-looking
building. Upstairs, a database…