A London Ambulance Service spokesman said:
"We were called at 8.39am today to reports of a patient taken unwell at London Bridge station.
"We sent two ambulance crews, a single responder in a car, our hazardous area response team and a duty manager.
"Our staff have assessed four patients at the scene who were taken unwell. Three of the patients have been taken to hospital."
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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.