Three-part series chronicling plot to blow up the House of Lords in 1605 features Game of Thrones actor Kit Harington.

The BBC’s new primetime drama, Gunpowder, was described as unnecessarily gruesome and brutal over graphic scenes of violence, which aired minutes after the watershed on Saturday night.

The three-part series chronicles the plot to blow up the House of Lords in 1605, with Game of Thrones star Kit Harington playing his ancestor Robert Catesby, the mastermind behind the plot.

The opening episode contained close-up scenes of a young priest being hung, drawn and quartered and a woman stripped naked before being crushed to death by a stone slab, prompting complaints from viewers.

One viewer said she felt “traumatised” by the “hideously brutal” scenes, while another commented: “This execution scene is one of the most painful things I’ve ever witnessed on TV.”

Sally Abbott, the lead writer on BBC1 crime drama The Coroner, said she thought Gunpowder – which began 10 minutes after the 9pm watershed – was a “very good drama”.

However, she said she felt compelled to change channels during the scene of a woman being stripped and tortured, which she said “made my heart sink”.

She said: “I thought it was a very good drama. It dealt with the persecution of Catholics terrifyingly. And we don’t often see that. I don’t want history to be disinfected and misrepresented but last night I had a really strong reaction to seeing a middle aged woman stripped and tortured. And some longer shots of her nudity than were needed.”

Abbott wrote on Twitter that broadcasters should “be careful *how* we show stuff” and added: “It’s too important a story to have people switch over & not continue [watching].”

Boyd Hilton, the entertainment director of Heat magazine, said he was surprised at how violent Gunpowder was, but that it was justified. “It was really extreme but I thought it was bold of everyone involved to make it that extreme,” he said.

“It was definitely clear that they went out of their way to show the hideous reality of how violent it was at that time and that was part of the story. They have to show how horrendous it was to show how riled up his character is and how that inspired effectively his terrorism of the gunpowder plot.”

The programme split viewers, who voted in a poll on the Radio Times website, with 52% saying it was “too gory” at the most recent update on Sunday afternoon.

Harington, whose character Robert Catesby is an ancestor on his mother’s side, said in interviews to promote Gunpowder that he thought audiences would accept “a greater level of violence as long as it’s justified”.

He added: “We can’t avoid the executions that the people around these men suffered. And I think it’s wrong when showing a torture scene or execution, I think it’s wrong to shy too far away from the reality of it. You need to feel the reasons, to know why they go and do the things they do.”

A BBC spokeswoman said: “The scenes aired after 9.30pm with a clear warning given to viewers before the episode started. The methods depicted are grounded in historical fact and reflect what took place during the time of the gunpowder plot.”

The regulator Ofcom said it would wait to receive any viewer complaints against the broadcasting code before deciding whether to investigate.