Mayor Boris Johnson will be in Croydon North today ahead of next weeks by-election in the seat.
He will campaign alongside Conservative Party candidate Andy Stranack.
On Thursday Ed Miliband will join Labour's campaign.
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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.