The mishap occurred while the judges were giving their responses to contestant Arisxandra's performance.
It was not the final's only unplanned incident, with the panel later being pelted with eggs by Natalie Holt, a member of the orchestra supporting Richard and Adam.
Holt said afterwards: "I want to apologise to Richard and Adam for overshadowing their performance. I've never done anything like this before and in hindsight I have realised it was a silly thing to do."
Attraction were the winners on the night, with Jack Carroll and Richard and Adam in second and third place respectively.
The show also featured Psy performing his latest hit 'Gentleman', while Taylor Swift and Ed Sheeran sang their new single 'Everything Has Changed'.
Photo gallery - Britain's Got Talent final in pictures: