Cult musical "The Rocky Horror Show" is to titilate London theatregoers once again, 40 years after the film it spawned first hit the silver screen, with extra dates announced Wednesday due to high demand.

Richard O'Brien, the show's creator, chose to reprise his camp musical in the Playhouse Theatre and will act as narrator, sharing the role with stars of British theatre such as Stephen Fry and Spice Girls singer Emma Bunton.

Fans snapped up all the tickets for the 11 originally planned shows in less than three days, forcing organisers to announce another eight new dates, tickets for which go on sale on Friday.

The production has also teamed up with human rights group Amnesty International for a gala evening on September 17.

The event will be broadcast live in European cinemas in support of Ihar Tsikhanyuk, a Belarusian drag queen who was beaten by police for campaigning for gay rights.

"'The Rocky Horror Show' is a fabulous celebration of freedom of expression -- a fundamental area of Amnesty's work," said Aikta Hancock, special events manager at Amnesty.

"This is a perfect opportunity to rally support for men and women like Ihar and to call for justice for all LGBTI people whose rights are under threat," she added.

Although a commercial flop when released in 1975, the film -- a homage to sci-fi and low-budget horror films -- gained a cult following when cinemagoers at midnight screenings across the world began acting out the script.

The film tells the tale of a newlywed couple who stumble upon a castle filled with bizarre characters, including "Transylvanian transvestite" scientist Frank-N-Furter and his creation "Rocky", the "perfect man".