Or is it caused by the dreadful rear-facing speakers used in modern flat-screen televisions which means the top end of the audio spectrum, which is where inteligability is held, is lost? It probably sounded fine in the dubbing theatre but put high quality sound through rubbish speakers and it'll sound rubbish. Just a theory.

Of course it's really the viewers' fault isn't it. I mean if they can't be bothered to get state of the art loudspeakers and audio systems! And of course if they have to watch the increasing amount of rubbish drama featuring dysfunctional people who actually do mumble in extremis then so be it. Come on!, don't bother! Get a life and like me stop watching BBC drama and start using the TV for what it was intended...entertainment and information. We all have enough troubles in our lives at times without this stuff on TV. As long as there are big audience figures for this trash the Beeb will go in making it.

Thanks for the replies, it's some comfort that it may be the source material rather than my ears.

I've just watched Ep1 of this and I couldn't agree more.  Alright I have " modern TV with flat speakers" as mentioned above but even with volume right up, so much dialogue was lost.  However when the programme finished, I was glad my "flat speakers" didn't get blown away with title music.  I can imagine the old PPM hardly moving for ages and then hitting 6s!  

I always make a complaint referring to the Production Guidelines. The more we complain............
From this
" If a programme generates a significant number of justifiable complaints, Audience Services will ask productions to re-mix the sound at their own expense."

And for the programme makers there's a tutorial here!

This is a subject dear to me as someone who throughout his life has emphasised quality in all I do.
My interest in high quality sound was a major influence in my aspiration to join the BBC at a time when it was admired throughout the world for its programme quality in most areas, and its at that time, wonderful technical research, particularly into loudspeaker design. At that time there was nothing commercially available which came near the quality of BBC monitors from about '65 to the late 70s.
I left the BBC in the early 70s because shift work did not agree with my constitution, and by the end of the decade was starting to be concerned about its staff's usage of intonation, it being often inappropriate, and I had often at that time wondered if the BBC had a 'Weird intonation department'.
I am afraid that that was only the start of a downhill trend in almost all areas, and sound quality has now plummeted to the level at which it is widely denigrated on many audio sites. When I left I became a programme maker, deriving actuality and mixing and editing to final programmes.
Although now retired, and with declining hearing, I have worked on loudspeaker design since about '85, and in recent years produced my best, which I use at home in my studio.
On occasions the SQ from the BBC is so poor that I would swear that there is no energy coming from my tweeters, (above 1.8KHz that is), and very often mic, positioning is so bad that proximity effects are predominant, they masking  the presence range with excessive bass.
This problem is marked on R4's Today, BBC2 and BBC4, in the latter music often being too high in the mix, maybe only a couple of dB below the speech. I always mixed it by at least about 8 to 10 dB down.
Unfortunately the lowering of standards applies to many other aspects of the BBC, and I prefer what it was when its logo was written in Italics.
Often the mixed-in music, probably from CDs, is so obviously better quality than the added programme content, that it contrasts massively.
A well know owner of a major loudspeaker company has complained to me that the BBC no longer uses sound engineers; I do not know if this is so, but I am of the impression that the BBC uses fresh graduate trainees to make cheap programmes, and that these do not have the necessary experience to know how to produce good sound.
My own system at home is now so good that CD quality is way above all broadcast SQ. I also have a recording made by another loudspeaker manufacturer in the BBC anechoic chamber before it was demolished, and my system reproduces it extremely well, showing that my own speakers are also good on speech.
The BBC will have to change drastically if it is to justify its position of receiving its funds by compulsory licence fee, which at the moment seems to go largely towards paying excessive salaries to 'celebrities', rather than actual content of programmes..

If I may add another post -the sound quality of the recent Night Porter -sundays BBC1 is excellent-proving it IS possible to get it right all of the time?