Speaking to ITV News ahead of tonight's switch on in Oxford Street, Jessie J said Christmas helped put London in a good mood - which was what the capital sometimes needed.
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With harmful pollutants at record levels the Mayor of London's campaign aims to highlight the impact air quality can have on health.
A firework was shot into a London bus sending frightened passengers running with fear.
Abdul Samad, 28, was stabbed outside his family home in Little Venice last night and died an hour later in hospital.