Boyle, who is favourite to win the show, is said to have become enraged after seeing her favourite judge Piers Morgan tell 12-year-old contestant Shaheen Jafargholi his was "the best singing performance we have heard in the semi-finals so far". (Watch more: Boyle sings way into final)
The comments reportedly set the Scottish singer into a rage as she thrust two fingers up at the TV screen and shouted "f*** off", before storming off to her hotel room.
About 150 people in the bar in the Wembley Plaza Hotel were said to be floored by the outburst.
"Everyone was stunned by her reaction," one witness was quoted in the Daily Mail as saying.
But Boyle's publicist rubbished the report, insisting she was not even in the bar when Jafargholi gave his performance.
"Susan was in the bar with friends but was getting hassled by a journalist," she said.
"The four of them left before Shaheen's live performance to watch it in the room instead."
Boyle, 48, became known around the world when a video of her debut performance on the show became a viral sensation online.
ninemsn 28 May 2009
You can take a girl out a Trailer Park, BUT you can NEVER take the Trailer Park out of a girl.
Just showing her origins.
There WERE better singers and in time, WILL be better ones in the future.
It's THAT simple.