Carys’s 11-year-old sister, Eliza, who plays the euphonium, will also perform at the Abbey. “I never thought I’d be able to play there in front of so many important people,” she said.
“Everyone should have a chance to play music.”
Among the guests in the Abbey are representatives of different generations.
That includes Saphia Turner, aged nine, winner of the BBC’s Make a Difference Young Hero Award, who sells artwork and carries out sponsored challenges to raise money for food banks.
D-Day veteran Jack Mortimer, who is 102 years old, is also expected to attend.
The Abbey has been decorated with specially made wreaths, with Berry and florist Simon Lycett helping to make them.
Among the musical performers are Melua, choristers from Westminster Abbey and a Cornish sea shanty group, Fisherman’s Friends, who said the invitation to sing was “the icing on the cake for us”.
The Together at Christmas carol concert will be televised and shown on ITV1 on Christmas Eve.