The Queen has watched a performance by the Script during her tour of the revamped Broadcasting House in central London.
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Greater Manchester Police said "inquiries are ongoing to fully understand the circumstances of the incident."
The US president enjoyed rousing support for his political agenda as a formerly hostile audience cheered his plans in office to the rafters.
The former leader said the party needed to learn lessons after his successor Paul Nuttall failed to unseat Labour in a hard-fought campaign.