According to reports, contestants including Lorraine Bowen had been preparing for their next performance when police arrived at the studios to order an evacuation.
A source told The Sun: "It was all incredibly dramatic and scary. Police came into reception and order everyone out immediately. No one was allowed back in and lots of people's cars have been left stranded behind police tape.
"Let's just pray they get this sorted as quickly as possible."
Builders working near Wembley Stadium discovered the unexploded bomb, which is believe to have been dropped over London by Nazi bombers in the 1940s.
Homes and businesses have been evacuated while army experts work to secure the area and dispose of the device.
A spokesman for the army said: "This bomb is a live munition in a potentially dangerous condition so it's important that people listen to the police and evacuate their homes if asked.
"We will do all we can to minimise the disruption but ask the public to bear with us - any bomb, even under a controlled explosion could cause significant damage to property and there is a genuine risk to life".
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