The Metropolitan Police says it's looking into whether the substance sprayed into the face of an officer may have been ammonia. He was attacked when he stopped a moped rider in Battersea yesterday afternoon.
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The London Marathon brings together thousands of people raising money for charity - not to mention some rather unusual costumes.
Planning on going to the London Marathon tomorrow? Read our handy guide first!
Celebrations to mark St George's Day have started in Trafalgar Square with feasts and tea to be found in abundance.