The headquarters of Britain's biggest Roma charity is a large building beside a major thoroughfare in east London, yet its official address is a P.O. box. The fear of reprisal against Britain's Roma community, even in London's most multicultural borough, remains real.

Hours after member of Parliament David Blunkett, the U.K.'s former home secretary, suggested last week that the arrival of Roma immigrants in Britain could trigger riots, an email was opened inside the headquarters of the Roma Support Group (RSG). It told the recipients to "f—k off," before adding that "every country in Europe hates [you] and we are no different."

The rhetoric of hostility toward the Roma throughout Europe is escalating, race relations experts say, lending credibility to the notion that it is the continent's most persecuted ethnic minority.