You’d be hard-pressed to call an hour spent in the company of Harry Shearer and Tom Leopold work. Not only is each a prolific comedian in their his right — Shearer best known for his roles in “The Simpsons” and “Spinal Tap” while Leopold has writing credits on numerous hits including “Cheers” and “Seinfeld” – but having known each other for more than half a century, they have a Statler and Waldorf-esque rapport that can turn even the most earnest conversation into a hoot.

The duo are in a particularly buoyant mood when we meet, at a rehearsal space in London, thanks to the upcoming premiere of their musical “Here Comes J. Edgar,” an endeavour that has been three decades in the making. Shearer and Leopold first wrote both the book and the lyrics alongside Peter Matz, Barbara Streisand’s musical director, who died in 2002, and it premiered on the radio in 1994 performed by Kelsey Grammer, John Goodman and Shearer’s “Spinal Tap” co-star Christopher Guest.

Over the decades, multiple attempts to turn the musical into a full stage show – and even a film adaptation – fizzled out before a chance conversation last year with the director of the King’s Head Theatre in London led to an offer. Now “Here Comes J. Edgar” is set to premiere at the 200-seat venue on July 10, directed by Josh Seymour with choreography by Bill Deamer.