It’s A Sin has just made history.

The Russell T Davies drama has reportedly been viewed over 6.5 million times on All4 – making it the service’s biggest ever instant box set.

According to the broadcaster, It’s A Sin is their “third biggest series to date” and their “most binged new series ever.” The first episode also became All4’s biggest drama launch on record.

Ian Katz, chief content officer at All4, said: “The extraordinary performance of It’s A Sin is a reminder that powerful drama with something important to say about the world can also be commercially successful.

“It has also demonstrated how our strategy of box-setting shows on All 4 can bring a greater combined linear and digital audience to a show than a traditional release pattern.”

It’s A Sin follows a group of friends in 1980s London who grow up in the shadow of the HIV/AIDS epidemic.

Olly Alexander leads the cast as 18-year-old Ritchie Tozer, who leaves his family home on the Isle of Wight to move to the Big Smoke in search of fame and success.

The Years & Years frontman is joined by newcomer Omari Douglas as Roscoe Babatunde, Callum Scott Howells as Colin Morris-Jones, Lydia West as Jill Baxter and Nathaniel Curtis as Ash Mukherjee. Neil Patrick Harris, Keeley Hawes, Stephen Fry, Tracy Ann Oberman, and Shaun Dooler also star.

The five-part has been praised across the board for its powerful storytelling, incredible cast, and bringing LGBTQ+ history to a mainstream audience.

In the latest episode of It’s A Sin: After Hours, Davies – who has lived with the idea for the series for decades – revealed the single moment in the drama that actually inspired its creation.

“There’s a key little moment where Gloria says to Jill, ‘I heard there’s a production of Seven Brides for Seven Brothers, and all seven brothers died.’ That’s a tiny little line that flies past you. The entire drama came from that,” he explained.

“I heard that story round about 1989 or 1991 – I can’t date it – and as a joke it’s kind of awful. It’s horribly funny and blackly comic – it’s profane at the same time.

“It just made me think, ‘Wow, imagine if there were seven brothers in a cast and they all got wiped out.’ That made me think, imagine if I had a flat full of people…”

Russell added: “It’s just one joke that looks like a throwaway moment. I didn’t tell David Carlyle [who plays Gregory/Gloria], the actors, or the director because I didn’t want to add too much weight. But that joke created the entire show.”

It’s A Sin airs at 9pm on Fridays on Channel 4, with all five episodes available to stream on All4 now. It will premiere in the United States on HBO Max from 18 February.

Related: It’s A Sin: Lydia West and Jill Nalder discuss the power of allyship during AIDS crisis.