The Olympic Park in Stratford has closed to visitors as the site is prepared for the start of the Games in a few weeks.
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Around 60 firefighters tackled the blaze at the four-storey building in Daleham Gardens, Hampstead, that broke out early on Tuesday.
It is the fourth time in five years that the London borough has topped the rankings, according to data from the ONS.
Catherine Burke's body was discovered at a house in a quiet street in Muswell Hill last Thursday evening.