Harman, who was last seen in the original West End cast of Shrek - the Musical at the Theatre Royal, Drury Lane in 2010, in which he played Lord Farquaad and for which he won a Laurence Olivier Award, is best known for playing Dennis Rackman in BBC TV's "EastEnders." His previous West End stage roles include Three Days of Rain at the Apollo Theatre, Sky Masterson in Guys and Dolls at the Piccadilly and Privates on Parade at the Donmar Warehouse.

Harman will play Simon Cowell. In a press interview in the UK's Daily Mail, Cowell commented, "The hardest thing was: how do you find someone who’s good-looking, talented and can look like me? And then we found Nigel!"

Erivo, who is currently playing Celie in the U.K. premiere of The Color Purple through Sept. 14, was recently also seen in the U.K. tour of Sister Act: The Musical, LIFT at Soho Theatre and in The Umbellas of Cherbourg at the Gielgud.

Previously announced with the title X Factor - It's Time to Face the Musical!, it has already undergone two workshops, and is written by stage and television comic Harry Hill (winner of three BAFTAs, seven British Comedy Awards and a Golden Rose of Montreux) and composer Steve Brown (previously represented in the West End by Spend Spend Spend).

According to press materials, I Can't Sing! goes behind the microphone and under the judges’ desk to reveal the (not necessarily accurate) story of heartache and laughter that keeps millions tuning in every week to the television talent show.  It is described as an affectionate poke at the world’s most talked about talent show that will please friends and foes of "The X Factor" in equal measure. The show will feature 19 original songs. In a press statement, Hill and Brown commented, "We’d been umm-ing and ahh-ing about the title for a while…then it hit us…'I Can’t Sing!'. It also happens to be the title of one of the funniest songs in the show and we hope hints at the direction we’re taking this production.  We think it’s also the only musical for a while with a singing hunchback, a talking dog and a man on an iron lung…but we’d have to Google that to be sure.  We're thrilled to be bringing this all singing, all dancing, all mickey-taking spectacular to the home of entertainment itself, The London Palladium.  We’re pretty certain that you won’t have seen anything like it before and it's great that Simon is backing it 4500%...Roll on March 2014!"

The musical will be presented by Stage Entertainment UK and Syco Entertainment, and directed by Sean Foley, whose production of The Ladykillers returns to the West End this summer. Foley has been seen on Broadway in the transfer of The Play What I Wrote, that he co-wrote and starred in from the West End. Co-founder of The Right Size, he has also been represented in the West End by Do You Come Here Often? and Ducktastic.

The creative team also includes choreographer Kate Prince (founder of ZooNation, whose shows include West End runs of Into the Hoods and Some Like it Hip Hop); designer Es Devlin (whose credits include the closing ceremony of the London 2012 Olympics, and creative director for Take That, Kanye West and the Pet Shop Boys stadium tours); sound designer Gareth Owen (whose credits include the Broadway transfers of A Little Night Music and End of the Rainbow from the West End); lighting designer Hugh Vanstone (Spamalot, Shrek, God of Carnage); and musical supervisor Phillip Bateman (Billy Elliot, Our House, Vernon God Little).

Stage Entertainment have previously produced Hairspray, Sister Act, Oliver!, Disney's High School Musical 1 & 2 and Fame in the U.K., and are currently also developing a stage adaptation of Made in Dagenham.

Syco Entertainment is a leading global music, television, film and digital production company. A joint venture between Simon Cowell and Sony Music Entertainment, with offices in London and Los Angeles, its shows include "The X Factor" (launched in the U.K. on ITV1 in 2004 and the U.S. in 2011 on Fox) and "Britain's Got Talent," as well as artists as diverse as One Direction, James Arthur, Leona Lewis, Susan Boyle, Il Divo, Labrinth, Loveable Rogues, Ella Henderson, Tate Stevens, Emblem3 and Fifth Harmony. Syco are also co-producers of the forthcoming One Direction movie, a group who emerged out of "X Factor."

To book tickets, contact the box office on 0844 811 0058, or visit www.icantsingthemusical.com for more details.