The officers are protesting against proposed changes to their pay and conditions.
Some 20,000 officers from all 43 forces across England and Wales are thought to be taking part in the first police march in the capital for more than four years.
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The elderly man has been remanded in custody after being charged with attempted murder.
A fire in a taxi closed roads around St Paul's Cathedral last night.
Young Londoners are finding it even more difficult to save for a deposit due to the inflating cost of rent.