Berezovsky emigrated to the UK in 2000 after falling out with President Vladimir Putin.
In fear of his life, he sought political asylum and moved to the South East of England, buying upmarket properties in Knightsbridge and Berkshire.
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The RMT union has accused Southern of inventing figures which the company claims show record numbers of guards are going sick.
Thursday morning's weather for the west of the region
Thursday morning's weather for the east of the region