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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A cloudy start to the short Christmas week. It's gong to be a mild one though with temperatures already above the double figure mark.
As we move into a shorter working week for most people, we are looking at a generally cloudy one.
Lots of cloud around today feeling relatively mild although it probably felt a bit cooler because of the breeze.