St Martin's Theatre is a West End theatre which has staged the production of The Mousetrap since March 1974, making it the longest continuous run of any show in the world. The theatre is located in West Street, near Shaftesbury Avenue, in the West End of London. It was designed by W. G. R. Sprague as one of a pair of theatres, along with the Ambassadors Theatre, also in West Street. Richard Verney, 19th Baron Willoughby de Broke, together with B. A. (Bertie) Meyer, commissioned Sprague to design the theatre buildings. Although the Ambassadors opened in 1913, construction of the St Martin's was delayed by the outbreak of the First World War. The theatre is still owned by the present Lord Willoughby de Broke and his family.