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.
More top news
70-year-old Stephanie Booth, a pioneer of gender reassignment, died when a tractor crashed down a bank on her farm.
Several supermarkets have announced fuel price cuts of 2p pence per litre
Mark Ashley Hughes was found in possession of a sawn off shotgun and a Tazer. He claimed he found them in his grandparents garden.