As of July 28th, Martyn Ellis and Simon Gregor will be replaced by Alan Perrin and Nigel Betts, according to the London Theatre Guide.
The central characters of Richard Hannay and Annabella Schmidt will continue to be played by Jo Stone-Fewings and Josefina Gabrielle.
Both of the new cast members have had extensive experience in showbiz – Betts may be particularly recognisable to many audience members after television appearances in Trial and Retribution, Silent Witness, A Touch of Frost and others.
Perrin’s theatre credits include The Trial, Richard III, Cyrano de Bergerac and Henry V for the Royal Shakespeare Company.
The 39 Steps first hit the stage at the West Yorkshire Playhouse in 2005 before having its London premiere at the Tricycle Theatre in August 2006 and moving to its current home at the Criterion Theatre the following month.
London visitors can book tickets for the play until February 2009.