According to People, the film crew posted warnings that the explosion would be taking place, but the large fireball that ripped off the roof of the bus could be seen from far away.
"The scale and realism of the explosion would have worried a lot of people who were quite a long way off and not able to see the film crew and cameras," Parliament member Nigel Huddleston told The Guardian. "Walking past parliament a few minutes later, some tourists clearly had no idea whether it was real or not."
The blast was especially worrisome as it stirred up memories of the 7/7 bombings in London that took 52 civilian lives on July 7, 2005. With this in mind, Huddleston tweeted a video of the explosion, letting his followers know that it was fake.