Balfour Beatty has won a contract worth £154 million to transform the Olympic Stadium in east London.
Last summer, Balfour was awarded the contract to convert the stadium roof and will now lead the remainder of the transformation work.
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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.