This video uploaded to You Tube appears to show slow-moving traffic at the border checkpoint between Gibraltar and Spain as cars are searched by officials last Friday.
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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.
The foreign secretary has criticised internet and social media giants for failing to detect and remove extremist material posted online.