By Keily Oakes BBC News Online entertainment staff

The tale of the demon barber of Fleet Street - a particular favourite with amateur operatic groups the world over - sees a rare outing for a musical on the Covent Garden stage.

Sir Thomas Allen, who plays Sweeney Todd, is known for his outspoken views

In general, the ROH leaves the musicals to the West End, but it has brought together a cast of opera stars for this production.

But it is taking a risk by staging the production because as a publicly-funded opera house it has a loyal core audience that expects the highest standards.

But according to director of opera Elaine Padmore, ticket sales are proving the ROH was right to be take a detour over the festive season.

Audience mix

Stephen Sondheim's creation is a complex production - a borderline musical/opera rather than a play with music.

It is expected to attract a mixture of regular opera-goers as well as those who may not have visited the famous auditorium before, according to Ms Padmore.

Composer Sondheim describes Sweeney Todd as a musical thriller

But she does admit the macabre nature of the story will not be to everyone's tastes.

"It is dark and dramatic, with a touch of cannibalism," she explained.

But with just nine performances being staged, the seasoned opera buff will not have long to wait before the usual fare of classics and ground-breaking productions return.

Sweeney Todd is a co-production with the Lyric Theatre in Chicago, which ran the show last year.

In the title role in the US was the Welsh singing sensation Bryn Terfel, who wowed the critics, and Ms Padmore is confident the Covent Garden stage is even more suited to the show because it is less cavernous than its Chicago counterpart.

For its London transfer an entirely new cast has been employed, with Sir Thomas Allen, known for his outspoken views on the arts, taking on Sweeney Todd.

Pie shop

He has previously accused opera singers of "dumbing down", criticising crossover artists such as Bond and Russell Watson in their populist approach to marketing their art.

The killer barber takes his revenge

The character of Sweeney Todd is cast out of society only to return to seek his revenge, killing his victims in his barber's chair before sending them down a chute to the pie shop below.

"Although it is a witty and clever script, there are not many laughs to be had when Sweeney Todd is around," said Ms Padmore.

Sondheim visited the cast and crew during the final week of rehearsals to cast his eye over the ROH's version of his famous composition.

"He is interested in the particular interpretations and making sure the integrity of the piece is being kept," said Ms Padmore.

Sweeney Todd at the Royal Opera House runs from 15 December to 14 January.