The Metropolitan Police wrote to Home Secretary Theresa May asking for the ban two days ago.
We have made this decision based on specific intelligence and information, and our message is clear - we do not want people coming into the areas to attend these events.
The three other boroughs affected are Tower Hamlets, Newham and Islington.
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Around 2,000 staff will be balloted, including those working in engineering, signals, electrical, track and control centres.