More than half of all TV viewers are having to watch with subtitles on because modern films and dramas are plagued by mumbling actors and poor sound, a study has found.

Research found 51 per cent of all viewers believe sound quality and mumbling on televisions is worse than ever before - and surprisingly, that figure remains the same across all age groups.

An astonishing 60 per cent regularly have subtitles on for certain shows, while one in four have them on for most shows, and 13 per cent have them switched on all the time.

The findings come after several BBC dramas like Sherwood, The Jetty, Jamaica Inn and even Happy Valley, sparked thousands of complaints over mumbling and indistinct audio.

Mumbling on TV shows has become a widespread issue caused by a mix of naturalistic acting styles and modern sound mixing that prioritises cinematic background audio over voices.

The study found that the main reasons for using subtitles include mumbling actors (31 per cent), too-loud background music and sound effects (29 per cent).

A quarter of Brits (26 per cent) say that they mainly use subtitles because they can't understand other British regional accents, with Londoners struggling the most to understand accents outside of their own, at a third (33 per cent).

Almost eight in ten (78 per cent) British TV viewers say that modern television programmes don't cater well enough to deaf or hard-of-hearing viewers, while half of Brits (51 per cent) say audio quality has become significantly poorer compared to older TV shows.

In 2016, the BBC's TV chief said it was 'incredibly hard' to fix mumbling by actors on popular dramas, such as Happy Valley.

Charlotte Moore, the £264,000-a-year controller of channels, at the time promised the corporation would investigate sound issues.

She said that complaints about mumbling after the first episode of Happy Valley saw producers head back to the edit suite to change the sound levels so the issue could be corrected quickly.

At the time, Happy Valley executive producer Nicola Schindler said viewers were partly to blame for the 'mumbling' problem, adding that they were not tuning their TV aerials correctly.

However, BBC director general Tony Hall ordered an investigation into mumbling, following hundreds of complaints about the series online.

The BBC previously said the real problem with Happy Valley was the Yorkshire accent.

'We worked very hard to ensure everything was audible while keeping the sense of reality and the rawness of performances,' a spokesman said at the time.

'Happy Valley is a drama that has been lauded for its realism and dramatic pathos – as such the dialogue is representative of the characters and area in which it is based.'

The show, in which Sarah Lancashire plays a hard-nosed policewoman, is set in West Yorkshire and filmed in and around Bradford and Huddersfield.

Unsurprisingly, the BBC's explanation went down badly with licence fee payers in the region, who said even they struggled to follow the programme. They accused the BBC of 'patronising' them with 'nonsense' excuses.

Even BBC bosses had a different explanation behind the scenes, the BBC Trust's minutes confirmed.

'Members discussed viewer complaints regarding audibility and sound quality on Happy Valley,' the record of the meeting stated.

'The director general noted that he took all such complaints seriously and had already asked BBC Television to look into this matter and consider any immediate issues as well as identifying any lessons for future commissions.'

And in 2013, Lord 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.'

To ensure an easy viewing experience, Narrative Entertainment, the owner of Great! has partnered with Encompass, an AI-assisted subtitling platform.

This platform delivers broadcast ready subtitles produced faster, more cost-effectively, and with greater accuracy than traditional methods, to benefit viewers of Great! channels - no matter the reason, they want subtitles.

This AI-powered subtitling platform is now available across all Great! Channels.

The findings come as Great TV brings back gripping US thriller series Sue Thomas: F.B.Eye, inspired by a real-life deaf FBI agent. It begins on Freeview channel Great Mystery this month.

Kate Gartland added: 'Sue Thomas: F.B.Eye is such a remarkable story, and we're thrilled to be bringing it back to UK screens, celebrating what an amazing trailblazer the real Sue Thomas really was.'