'Sherlock' Hits Ratings Low in U.K.

Benedict Cumberbatch in 'Sherlock'

The BBC's hit show with Benedict Cumberbatch and Martin Freeman attracted an audience of 6 million on Sunday.

Is Sherlock losing its charm?

The BBC's hit show, starring Benedict Cumberbatch and Martin Freeman, drew its lowest-ever overnight U.K. ratings, attracting 6 million viewers on BBC One on Sunday night, according to data published Monday by Broadcast magazine.

The previous lowest-rated episode of the drama in Britain had been the second of season one, which drew an average U.K. audience of 6.4 million. However, that episode's 25.6 percent share of the total U.K. TV audience at the time was lower than Sunday's 27.4 percent share.

The ratings for the hit drama always rise sharply in the consolidated ratings for a full week.

The Sunday audience for the second 90-minute episode of season four, titled "The Lying Detective," came in well below the 8.1 million viewers for season-opener "The Six Thatchers" a week earlier. That in turn had been down 1.1 million from the season-three opener in 2014, but only slightly below the audience reached by Victorian-era one-off "The Abominable Bride," which aired Jan. 1, 2016.

With a full week of audience data now in, The Six Thatchers was the most watched program over the festive season across all  U.K. channels with 11.3 million viewers, according to consolidated viewing data issued Monday by the BBC. It achieved a consolidated audience share of 37.8 percent.

Last year, Sherlock: The Abominable Bride topped the festive ratings, with 11.6 million viewers.

Sherlock, which in the U.S. airs on PBS, is produced by Hartswood Films. Steven Moffat and Mark Gatiss are writing and executive producing the series.

It remains unclear whether the show will return for a fifth season. "We absolutely don't know," Gatiss said after a BBC screening of the first episode of the current season late in 2016. "It's up to all kinds of factors, scheduling and willingness to do it."

He concluded: "We are just not sure."