This seems to have become a very fashionable thing to say.

In answer to almost anything.

Have you noticed this too ?

I haven't noticed this, Ali, but perhaps we're a bit behind the times in my part of the woods. Are you sure they're not saying: "Yeah, I know", like the man in the wheelchair in Little Britain?

Tone

Keep listening Toneee.

My work colleagues are saying it a lot (Suffolk)

as well as my friends around Chelmsford.

Perhaps it's rather trendy.

Thanks for being you Toneee.

Alison  

I've heard it issuing from My Own Mouth on occasion. And been suitably horrified. 

I was amused to hear a chap talking on his mobile in Lyon a couple of years ago confirm that it's not confined to English: "Bah oui, non, c'est clair", he said, and I think I stifled my laughter in time. I have also heard "ja, nein" from time to time.

So the confusion would appear to be spreading. 

Russian's had the marvellous "da-nyet" (as a more emphatic form of "nyet") for as long as I can remember.

German has a form that's a bit like that. In Mahler 3 there's the line 'du sollst ja nicht weinen'.

You're evidently too immersed in popular culture, Alison. Repent now and immure yourself in the safety of (most of) Radio 3. As they say, 'you need to get out less'.     

Dundonians have a habit of saying 'Eh, no?' at the end of questions, e.g.: "It's a bonnie day the day, eh no? (Quite pleasant today, is it not?)"

What makes it particularly relevant to this thread is the fact that the 'eh' sound here doesn't equate to 'eh' as in 'eh, what?' Down South, but is a unique Dundonianism; the 'eh' sound is used where the rest of the UK uses 'I' (or increasingly 'oi'). As in what you have for lunch ('a peh'), what you have at the pub ('a peh anna pehnt'). So this 'Eh, no?' is literally 'Aye, no?', which is as close as damnit to 'Yeah No' as can be - except that they've been saying it for decades if not centuries.