Directed by Phyllida Lloyd, the cast for the staged reading will be: Hugh Bonneville (Giles Ralston), Nicholas Farrell (Major Metcalf), Iain Glen (Sgt Trotter), Tamsin Greig (Mollie Ralston), Miranda Hart (Miss Casewell), Harry Lloyd (Christopher Wren), Patrick Stewart (Mr Paravicini) and Julie Walters (Mrs Boyle).
Hosted by Agatha Christie's grandson, Mathew Prichard, the show will also be the 25,000th performance of The Mousetrap.
All of the proceeds from the night (which is already sold out) will be donated to Mousetrap Theatre Projects, the theatre education charity seed-funded by the play, which has been the world's longest running stage production since 1958.
Before the Gala begins, the Lord Mayor of Westminster, Mathew Prichard, and producer Stephen Waley-Cohen will unveil a permanent Memorial to Dame Agatha Christie at St Martin's Cross in the form of a giant book also containing her portrait.
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