UTV's Marc Mallett says that tensions in Northern Belfast have been running high for weeks ahead of Monday's violence.
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The first direct freight train linking China and the United Kingdom will arrive at its final stop in London later today.
The Prime Minister said Parliament will be given a binding vote on the final deal, but said the result will not stop Britain leaving the EU.
Officials from the train drivers' union Aslef will meet managers from Southern Railway, whilst the RMT will meet separately with Acas.