As a child performer, she starred on TV in "Opportunity Knocks" and "Just William," before appearing onstage with Angela Lansbury in Gypsy in 1974. As an adult, her credits include the original cast of Cats, and West End runs of Chicago, Guys and Dolls and 9 to 5 on tour.
The role of King Arthur is currently being played by Joe Pasquale, whom Langford contacted on Twitter to invite him to see the show, and then suggested his casting to the producers.
Daniel Boys, a finalist in BBC1's "Any Dream will Do" to find a performer to star in Joseph and the Amazing Technicolor Dreamcoat, has appeared in tours of Rent and War Of The Worlds and in the West End in Avenue Q.
Pasquale and Langford appear through March 22. To book tickets, which are on sale through April 12, contact the box office on 0844 871 7627 or visit www.spamalotwestend.co.uk.