The Abba pair will join the cast of Mamma Mia! to mark the show's 15th birthday
Henry said the award felt like a 'validation' after nearly 40 years as a comedian
Other winners included Rory Kinnear, who won Best Actor and Most Promising Playwright
As part of a new series, we take a closer look at some of the WhatsOnStage Awards categories, starting with the Autograph Best Original Music Award.
Actor Julian Glover's extensive work on stage includes the lead in The Voysey Inheritance (National Theatre), King Lear (Shakespeare's Globe), Richard II (Old Vic) and Oliver! (West End). He is currently appearing as The Interlocutor in The Scottsboro Boys at the Young Vic
Susan Stroman's production of The Scottsboro Boys opened at the Young Vic earlier this week. Starring Julian Glover, Kyle Scatliffe and Colman Domingo, it runs until 21 December
Strictly star Natalie Gumede was among those at the opening night of The Scottsboro Boys at the Young Vic Theatre last night (29 October 2013). Directed by Susan Stroman, Kander & Ebb's final musical runs until 21 December