Mick Cash, from the RMT Union, says that he does not believe that Londoners want fundamental freedoms - such as the right to strike - to be eroded.
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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.