A Government spokesman said:
We are currently experiencing temporary IT problems which may add to the time taken to conduct passport checks.We are working to rectify this issue and are providing extra staff to get passengers through the controls as quickly as possible. Our priority remains security of the border.We apologise for any additional time this adds to passengers' journeys.
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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.