The penultimate episode of Line of Duty was the show’s most-watched instalment to date, with an average of 11m viewers tuning in on Sunday night.
The record ratings came as BBC One unveiled a trailer for next weekend’s series finale, that suggested it may be the police drama’s last ever episode.
“Every investigation has led to this,” the promo declared.
A lingering H in the caption hinted that the mysterious criminal mastermind known as ‘H’ would be unveiled at last.
Line of Duty returned to TV screens in March with 9.6m viewers watching the series’ first episode – up on the 9.07m who tuned into the previous series’ finale.
Sunday’s episode saw Kelly Macdonald’s character, Joanne Davidson, subjected to a mammoth grilling that led to secrets about her background being revealed.
It commanded 51.7% of the UK’s TV audience, according to overnight figures.
It was the highest overnight audience for a drama since Doctor Who’s Christmas Day special in 2008, which was watched by 11.7 million viewers.
Macdonald was tight-lipped about the series finale when she appeared on BBC Breakfast on Monday, giving a terse “no comment” to presenter Dan Walker’s demands for plot information.
Yet she did reveal that filming one dramatic scene had descended into laughter when one of the cast mispronounced “racist thugs” and said “racist slugs” instead.