Dai Davies, the former head of royal protection for the Metropolitan Police, says accidents like these are embarrassing for the service, but that training for officers is very rigorous.
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A fine day will then follow with plenty of sunshine and light winds.
In this episode, Andrew Price is in north Wales discovering how an underground power station helps to keep the lights on across the UK.
More than 3,000 fewer people died from the effects of stroke between 2010 and 2012 compared to a decade earlier, according to a new report.