Many West End venues (especially ATG and LW theatres) now offer pre-order services like Smart Waiter or in-seat ordering. You can order interval drinks ahead—either before the show or via email link—and collect from a designated counter during the break. It’s a real time-saver that avoids frantic queuing.
Even the Royal Shakespeare Company does this with an email link that arrives days in advance. They’ll make sure everything is ready for you at interval. I’ve also used it at the Piccadilly and Lyceum with zero hassle.