‘Harry Potter’ star Jason Isaacs claims the young cast drank ‘at an industrial pace’

Mischief not managed.

Jason Isaacs, who starred as Lucius Malfoy in the “Harry Potter” movies, said that the young cast was drinking at “an industrial pace.” 

The franchise starred Daniel Radcliffe, Rupert Grint, Emma Watson and Tom Felton.

“It was always strange going back to the films, where they were a couple years older than the last time I saw them, and I would treat them how they had been previously,” Isaacs, 60, told The Post while promoting his BritBox miniseries “Archie,” where he played Cary Grant. 

“So, treating a 14-year-old like a 12-year-old wasn’t great,” he said. 

“And, when they were 18, and we treated them like they still weren’t allowed to smoke or drink — and, they were doing both at an industrial pace — that was odd.”

Radcliffe, 34, has previously spoken about struggling with drinking problems in his youth. 

Radcliffe — who recently became a new dad when he welcomed a son in April with his longtime partner, Erin Darke, 39 — previously said he has been sober since 2010. 

During a 2020 BBC Radio 4 interview on “Desert Island Discs,” Radcliffe said, “If I went out and if I got drunk, I’d suddenly be aware of there being interest in that because it’s not just a drunk guy, it’s ‘Oh, Harry Potter’s getting drunk in the bar …’”

And his way of dealing with that, he said, “was just to drink more or get more drunk, so I did a lot of that for a few years.”

“A lot of drinking that happened toward the end of Potter and for a little bit after it finished, it was panic, a little bit not knowing what to do next — not being comfortable enough in who I was to remain sober,” he said, adding that his family and friends gave him “enough perspective on my life” to get sober.

In 2012, Radcliffe said that drinking had been “unhealthy and damaging” to his body and social life.

“I was living in constant fear of who I’d meet, what I might have said to them, what I might have done with them, so I’d stay in my apartment for days and drink alone,” he told Shortlist magazine. “I was a recluse at 20. It was pathetic — it wasn’t me. I’m a fun, polite person, and it turned me into a rude bore.”

Felton, 36, who played Draco Malfoy — Isaacs’ fictional son – has also openly spoken about his struggles with addiction.

“Drinking becomes a habit at the best of times,” Felton wrote in his 2022 memoir, “Beyond the Wand: The Magic and Mayhem of Growing Up a Wizard.” “When you’re drinking to escape a situation, even more so. The habit spilled out of the bar and, from time to time, on to set … It came to the point where I would think nothing of having a drink while I was working. I’d turn up unprepared, not the professional I wanted to be. The alcohol, though, wasn’t the problem. It was the symptom.”

He described in his book how his agents, managers, lawyer and former girlfriend Jade Olivia staged an intervention and a made a plan to send him to rehab. 

“Everybody in the room had written me a letter,” he recalled. “I listened to Jade and the others as they told me how concerned they were about my behaviour, about my drinking and my substance abuse. I was in no state to hear them.”

The letter that “hit the hardest” was from his lawyer, the one person in the room he “knew the least.” Felton recalled: “My lawyer, whom I’d barely ever met face to face, spoke with quiet honesty. ‘Tom,’ he said, ‘I don’t know you very well, but you seem like a nice guy. All I want to tell you is that this is the seventeenth intervention I’ve been to in my career. Eleven of them are now dead. Don’t be the twelfth.’”

Isaacs, who will soon star in Season 3 of the Emmy-winning HBO series “The White Lotus,” further told The Post about Radcliffe, Felton and their former “Harry Potter” co-stars, “What’s odd is when people say to me, ‘Is it strange, them growing up?’ It would be extremely strange if I met them and they were still 12!” 

“I saw Rupert recently, and they looked incredibly happy,” Issacs said, referring to Grint, 35, who welcomed daughter Wednesday in 2020 with his longtime partner, actress Georgia Groome. 

“I speak to Tom all the time; he doesn’t have kids yet. I know Dan is a dad,” said Issacs. “How do I feel about it? They’re all men and women, and very accomplished in whatever field they are, and it’s always lovely to see them.”