Since Hamilton debuted in New York in 2015, the hip-hop musical, which transferred to the West End in London this month, has been breaking the conventions of musical theatre with award-winning abandon.

There was the subject matter: the story of America’s least well-known founding father Alexander Hamilton; and the music: a fusion of rap, hip-hop and classic theatrical numbers. And, controversially, there was the diverse cast, with young black, Asian, Latino and mixed-race actors portraying the old white founding fathers and their cohorts.

The director of Hamilton, Thomas Kail, said there was “no question” the multiracial casting would also be at the core of the UK version, which officially opens on 21 December.

“We never imagined casting the show in any other way – never for one second,” he said. “We are very conscious of what we are doing here. This is not colour-blind casting. It felt essential.”

Kail’s relationship with Hamilton’s celebrated writer, Lin-Manuel Miranda, began in 2005 when he directed Miranda’s debut, the musical In The Heights. He was also one of the first to witness the origins of Hamilton, which began as a single song in 2009. With Kail’s encouragement, the song grew into a 10-track mixtape and eventually spawned an ambitious 46-song musical.

Hamilton might begin in 1776, but Kail said he and Miranda always intended for the show to feel relevant, holding up a mirror to society. In the original production, Miranda, who is of Puerto Rican descent, played Hamilton; in London, Jamael Westman, born to an Irish mother and Jamaican father, takes on the role.

Hamilton originated as a single song inspired by Miranda’s reading of a biography on the founding father. Composed in 2009, My Shot was first performed during a visit to the White House. It wasn’t until Kail watched the song being performed to an audience at a New York benefit gig in a small theatre in 2012, that he experienced his “thunderclap moment”.