Singers Annie Lennox and Radiohead frontman Thom Yorke, as well as actor Ewan McGregor, have all shown their support to six activists who have been climbing the Shard in protest of oil drilling in the Arctic.
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A lamp in the tower which houses Big Ben is to be switched off for the first time in more than 70 years.
Sir Bruce entertained audiences for more than seven decades.
Work in the tower will also pause over the bank holiday weekend.