Every day, police officers across the capital put themselves in danger.
And in memory of those who've been killed in the line of duty, this morning a group from the Metropolitan Police joined a charity cycle ride starting at the Police Memorial, on the Mall.
Clare Fernyhough reports.
Two widows are part of a team cycling from the National Police Memorial on The Mall to the National Arboretum in Lichfield.
Jo Hill and Nikki Dent are raising money to go towards the building of a memorial wall at the Arboretum to honour all officers killed in the line of duty.
Jo's husband, PC Nicholas Hill, died in May 2002 at the age of 27, after a motorcycle accident while reporting for duty.
Nikki's husband, PC Christopher Dent, died in April 2009 at the age of 36, after a car and his motorcycle crashed.
The riders hope to arrive in Lichfield on Sunday.