By Ella Wills and Emma Saunders, May 3 (BBC): The final episode of Line of Duty was the BBC show's most-watched one to date, with an average of 12.8 million viewers tuning in on Sunday night.

The BBC said it was the most-watched episode of any drama since modern records began in 2002, although that does not include soaps.

Viewers tuned in to find out the identity of criminal mastermind, H.

The finale commanded 56.2% of the UK's TV audience, according to overnight figures.

The five-minute peak audience was 13.1 million, between 21:45 and 21:50, which was the end of the interrogation of the "fourth man/woman", and its aftermath.

The last time a TV drama got higher overnight viewing figures was an episode of Heartbeat in February 2001, which had an overnight audience of 13.2 million.

Overnight viewing figures are generally not considered as relevant as they used to be, given the increase in on-demand services and changing viewer habits but Line of Duty has bucked the trend, with fans keen to watch live to find out the latest plot twists and avoid spoilers.

Almost four million more people tuned in to Sunday's episode compared with the previous series' finale, which was seen by 9.07m in 2019.

The show - which first aired in 2012 - was created by British writer Jed Mercurio, and stars Martin Compston as DI Steve Arnott, Vicky McClure as DI Kate Fleming. and Adrian Dunbar as Superintendent Ted Hastings and Kelly Macdonald as DS Joanne Davidson.

Charlotte Moore, BBC's chief content officer said: "Addictive event television, Line of Duty has kept the nation guessing for the last seven weeks, so it's no surprise that last night's jaw-dropping finale set a rating record.

"Jed Mercurio is a master of his craft, and I would like to congratulate him and the entire cast and crew for delivering such an incredible drama series. I'm looking forward to having a conversation with the team about where we go next and what the future of the series might be."

But despite high interest in the finale, reviews for the series finale were decidedly mixed.

So what did the critics make of it?

Kelly Macdonald (r) was a newcomer in series six, playing acting DS Joanne Davidson

The episode saw the much-anticipated unveiling of mysterious criminal mastermind H as DCI Ian Buckells, played by actor Nigel Boyle.

The future of anti-corruption unit AC-12 was also left hanging in the balance. But the ending left some disappointed.

Metro's Harry Fletcher said Line of Duty's "frustrating" series six ended in a "whimper".

"Its usual complexity seemed to go out of the window during the pivotal interrogation scene with Ian Buckells (Nigel Boyle), which saw him unmasked as the Fourth Man [also known as H]," he wrote in his three-star review.

There were "flashes of [the show's] usual brilliance" in the finale, he said, but it "left plenty of questions, with narrative arcs tossed aside with abandon".

"Sunday's installment felt like an ending of sorts, despite the fact there may well be more episodes in future," he said.

"But will anyone be talking about the Line of Duty series six finale in a decade's time, or even remember how the dullest cop in the service was revealed as the big bad?"

Ian Buckells was revealed as mystery criminal H

In another three-star review, for The Guardian, Lucy Mangan cited the unveiling of H as evidence that series six of Line of Duty has "superficially at least, delivered".

But she still suspects that the big reveal, for many, will have been an anti-climax. And, looking back on the series as a whole, Mangan wanted more.

There were plot holes throughout the season, she wrote, adding that the show had lost key elements along the way - including the connection between Kate and Steve.

"It was all fine," she wrote. "But, oh my, you should have seen it when it was good."

In the New Statesman, Rachel Cooke's review ended with a similar thought.

"It was, for a while, the greatest cop show ever made - and then, suddenly, it wasn't any more," she wrote. "Whimpers all round. Especially from me."

On a more positive note, The Times' Ben Dowell gave the finale four out of five stars - saying it gave viewers "a greatest hits compilation: a prison van interception, pistols drawn, plus a faint whiff of the political parable".

While he admitted the reveal of H as Buckells was "hugely disappointing on one level", he argued, "at least this felt plausible".

"Of course, it was staring us in the face all along," he wrote. "We knew H couldn't spell, and it was this lapse which 'definitely nailed him, thanks largely to a forensic search of police records that AC-12 could have done ten episodes ago.

"We wouldn't have had as much fun, though."

In the Daily Mail, Jan Moir said the conclusion did not let her down - describing the show as "a richly satisfying final episode, one that made up for the longueurs of previous weeks".

"Many loose ends were tied up," she said. "Although one big question remains: Will there be another series?"

Boyle revealed he was shocked when Mercurio told him he was the "fourth man".

"I was buzzing with excitement! I never suspected it because I know how Jed leads people down the garden path with really good red herrings, so I didn't really pay too much attention to things like Buckells' golf clubs, etc., but clearly, I should have done!

"I'd fully bought into the idea that Buckells was low on competence levels but looking back it all makes sense."

He added: "I've been sitting on it for a long time. The only person I told was my wife, nobody else, I know how much is at stake!"

Anna Maxwell Martin reprised her role as Detective Chief Superintendent Patricia Carmichael in the series. Photo - PA MEDIA

On Twitter, however, most viewers seemed disappointed.

One viewer, Louis Molyneux, wrote: "We waited a decade for Buckles to be H?" TV presenter Piers Morgan labeled the ending "a tad underwhelming". Chef Michael O'Hare called the ending "horrendous".

At one point, #fuming was trending in the UK - seemingly as a response to the reveal of H. "Think we need a public inquiry into the systemic failings of the finale... #fuming", wrote one poster.

Meanwhile, unimpressed Times Radio presenter Matt Chorley linked the audience's reaction to the protests at Manchester United's ground on Sunday.

"BREAKING: Thousands of angry fans gather outside the Line of Duty stadium," he wrote.