Hillary Clinton's coronation as the Democratic presidential candidate was set to be overshadowed by walkouts and sit-ins amid fresh allegations of dirty tricks against her left-wing rival Bernie Sanders.

On the eve of the party's convention in Philadelphia 20,000 emails were made public by Wikileaks showing supposedly neutral senior party officials tried to undermine Mr Sanders's insurgent left-wing campaign by publicly portraying him as an atheist.

Convention delegates supporting Mr Sanders, with whom Mrs Clinton fought an acrimonous primary battle, threatened protests, and his supporters planned marches outside the hall including delivering a coffin signifying the party was "dead" to them.

Norman Solomon, a Sanders delegate to the convention from California, told the Washington Post: "The outrage is not just smouldering, it is burning. There has been an insurgency in the party far beyond anybody'’s expectations."