Boyle, a 48-year-old church volunteer whose frumpy appearance hides a soaring voice, sang her signature tune 'I Dreamed A Dream' from musical Les Miserables as part of a tour of the talent show that made her famous.

There were doubts as to whether she would perform in the 'Britain's Got Talent' live show in the Scottish city after she pulled out of an event in Manchester, northwestern England, on Sunday night.

Two weeks ago, Boyle was rushed to a London health clinic suffering from exhausion. Her treatment followed her defeat in the talent show despite a global following on video-sharing website YouTube.

However, her fans in Glasgow were not disappointed on Monday night, with one, 39-year-old Audrey Hinde, saying afterwards: 'I thought she was fantastic. She brought tears to my eyes. She didn't seem under pressure at all.'

A clip of Boyle singing 'I Dreamed A Dream' is now reportedly one of the most watched ever on YouTube. -- AFP