Hundreds more viewers have complained about BBC drama Jamaica Inn despite the corporation saying it had adjusted sound levels "to address audience concerns" after viewers complained of being unable to hear some of the dialogue.

A total of 252 people complained after the second episode on Tuesday night (April 22), following the 546 who complained after Monday night's opening episode, with viewers saying t hey had to switch on the subtitles or turn up the volume to the maximum setting to understand what was being said.

A BBC spokeswoman apologised and said: " We are adjusting the dialogue levels in episode two and three to address audience concerns so they can enjoy the rest of the drama and would like to apologise to those viewers who were affected."

The TV adaptation of Daphne du Maurier's classic gothic novel, starring Downton Abbey actress Jessica Brown Findlay, initially pulled in 6.1 million viewers but has lost 1.6 million since then.

Emma Frost, who penned the screenplay, suggested that a technical fault, rather than the way that the cast delivered the lines, was to blame.

"No surprises here - I'm told there was a major sound problem for tonight's broadcast of Jamaica Inn - not surprised you couldn't hear it," she wrote.

The complaints come almost a year after BBC director-general Tony Hall said the corporation could look at how to stop actors ''muttering'' in its TV dramas.

"I don't want to sound like a grumpy old man, but I also think muttering is something we could have a look at," he said. "Actors muttering can be testing - you find you have missed a line... you have to remember that you have an audience.''

He said that the corporation was addressing the problem of background music making it difficult for some, particularly older viewers, to hear what was being said.

The drama, set in 1821 against the windswept Cornish moors, was directed by Philippa Lowthorpe, whose credits include Call The Midwife.

The three-part series follows Mary Yellan who is forced to live with her aunt and domineering uncle following the death of her mother.