Unite leader Len McCluskey has urged Labour to prepare for an early general election because of the strength of public feeling against the austerity measures imposed by the Government.
McCluskey also warned that there will be more industrial action over pay, pensions and cuts to public services.
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The violence began after a counter-protester allegedly doused a female rally organiser with pepper spray.
As temperatures climb through the day, the warmest spots are likely to be across western parts of Northern Ireland and western Scotland.
Boris Johnson and Amber Rudd have both criticised social media giants for failing to detect and remove extremist material online.