Image caption Did time finally run out for DCI Roz Huntley (Thandie Newton)?

The fourth series of BBC police drama Line of Duty came to an end on Sunday by revealing key information about the mysterious "Balaclava Man".

Viewers also saw what appeared to be the last of Thandie Newton's DCI Roz Huntley, the target of AC-12's latest investigation into police corruption.

The Guardian praised the show's "great acting and writing" while the Telegraph called it "insanely gripping".

A fifth series of the drama has already been commissioned.

Image copyright @Line_of_duty Image caption The makers of Line of Duty posted this tweet on Sunday showing cast members Martin Compston, Adrian Dunbar and Vicky McClure

ITV broadcaster Susanna Reid was among those to salute the season finale on Twitter, describing it as "suspenseful, stimulating, superb television".

"THANK YOU so much each & every one of you for watching," wrote cast member Vicky McClure. "It's been an absolute joy seeing your response over the last 6 weeks!"

Overnight ratings show that Line of Duty fetched an average audience of 7.46 million on BBC One, way ahead of the 3.79 million who tuned into Grantchester on ITV.

World Productions, who make the show for the BBC, said the ratings were "the highest live audience ever for the show".

Spoiler warning: do not read any further if you have yet to see the final episode of Line of Duty.

Image caption The show featured a stand-off involving Dunbar, Compston and McClure's characters

At the end of Sunday night's episode, it was revealed that "Balaclava Man" was not one person but several people working for a mysterious criminal network.

One of the balaclava-clad men was shot dead by police in a tense stand-off and was described as "a known violent criminal with long-term associations".

An AC-12 police report briefly shown on screen revealed his name to be Robert Denmoor.

The episode also saw Newton's character finally confess to her role in the death of forensics expert Timothy Ifield (Jason Watkins).

But she did not go down without a fight, ensuring her husband's lawyer Jimmy Lakewell (Patrick Baladi) was arrested for perverting the course of justice.

The episode ended with both characters in prison and Assistant Chief Constable Derek Hilton (Paul Higgins) dead in what appeared to be a staged suicide.

According to the Mirror's TV critic, the only flaw in the "tense and twisting" hour-long final was that it "wasn't long enough".

Media playback is unsupported on your device Media caption Actress Maya Sondhi who plays Maneet Bindra in Line of Duty tells Today plot twist was a shock to her

Actress Maya Sondhi, who played WPC Maneet Bindra in the series, told Radio 4's Today programme earlier that writer Jed Mercurio had yet to start writing the fifth series.

She also revealed that it had been "a shock" to find out in episode four that her character had been secretly feeding information to ACC Hilton.

"He does write amazing twists, doesn't he?" she said of "evil genius" Mercurio.

"The beauty of his writing is there are so many layers to it."

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