Perrin and Betts will take over as Man 1 and 2, respectively, July 28. They will join Josefina Gabrielle and Jo Stone-Fewings, who remain in the roles of, respectively, Annabella Schmidt/Pamela/Margaret and Richard Hannay. Perrin's theatre credits include His Dark Materials, The Trial, Gilgamesh, Richard III and Napoli Millionara for the National Theatre; Cyrano De Bergerac and Henry V for the Royal Shakespeare Company; and Ethel and Earnest, The Man Who… and Ritual in Blood for Nottingham Playhouse. His TV credits include "The Bill," "Wing and a Prayer," "Prime Suspect" and "Wycliffe"; on film he has been seen in "Feast of July" and "Dark Corners."

Betts' theatre credits include Tinderbox for the Bush Theatre; A New Way to Please You, Thomas More and Night of the Soul for The Royal Shakespeare Company; Eden End and Macbeth for West Yorkshire Playhouse; and Neville's Island for Watford Palace. His extensive television credits include "Trial and Retribution," "Silent Witness," "Midsommer Murders," "A Touch of Frost" and "Grease Monkeys" as well as regular appearances on "The Catherine Tate Show." On film his work includes "Chain Mail," "In Your Dreams" and "Mrs Ratcliffe's Revolution."

The 39 Steps is currently also playing on Broadway at the Cort Theatre, on tour in the U.K., in Italy, Israel, Australia, Korea, Germany and Greece, and is licensed to a further 15 countries around the world including Japan and Hong Kong.

To book tickets for the London production, contact the box office at 0844 8471778.