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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The London property market is expected to be the hardest hit as buyers sit it out to see how the economy will be affected.
The former London mayor paid tribute to David Cameron just hours after the Prime Minister announced his resignation.
The pound crashed to its lowest level in 30 years as Britain voted to leave the EU.