Conservative Party chairman Grant Shapps has called on Ed Miliband to "come clean and publish Labour’s report into the Falkirk selection in full."
Mr Shapps added, "It’s clearer than ever that [Unite chief] Len McCluskey is calling the shots in the Labour Party."
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Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.
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.