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 painting, entitled 'Beautiful Beautiful George Michael Love Painting', was auctioned to help raise funds for HIV and Aids prevention.
The 38-year-old victim was standing on a busy Victoria Line train when another passenger approached him.
The boy, called Roman, told police call handler his mum "is dead" and "she's closing her eyes and not breathing".