A man shouting and holding knives has been tasered by police outside Buckingham Palace.
The drama unfolded as hundreds of tourists and Londoners gathered to watch the changing of the guard.
A warning - Nick Thatcher's report contains footage that some viewers may find upsetting.
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A teenager has been airlifted to hospital after being stabbed outside a DLR station in south-east London.
By law, the Met Police has a duty to police public land outside grounds - that's costing them £9.3m a season.
John, who began running for Age UK back in the 1980s when he was aged 53, has raised an incredible amount since then - more than £40,000.