Shadow business secretary Chuka Umunna, the Labour MP for Streatham, wrote on Twitter: "Deepest condolences to the family of the lady tragically killed at a bus stop on Streatham High Road early this morning."
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PC Keith Palmer, 48, stabbed by Khalid Masood while on duty in the grounds of the Palace of Westminster last Wednesday.
Those gathered on the bridge fell silent at 2.40pm - the time the first call was made to police exactly seven days ago.