The Labour Party is convulsed by an internal crisis over anti-Semitism – whether it exists in the organisation, and if so, how widespread is it, and what to do about it. What has inflamed the controversy is the slow and rather off-hand reaction of the leadership. Jeremy Corbyn and those around him, with the possible exception of the Shadow Chancellor John McDonnell, have preferred to see the hand of anti-leadership conspirators behind the row, rather than take it as seriously as it demands.

Anti-Semitism, which has been called “the longest hatred” as it pre-dates Christianity by at least 300 years, is a dangerous and contagious virus. It can lie dormant for years, waiting its chance to surface. Any institution that begins to be infected by it must act firmly and quickly to suppress it. In Labour’s case the infection still appears to be marginal, at the fringes of left-wing politics and in some inner-city communities where Labour has come to rely on Muslim support. But it must be dealt with and so far it has not been.