I have a UHD box at home with an Onkyo Home Cinema set up - I usually have the UHD box connected by HDMI straight into the Onkyo - the sound coming through is DD.
I usually watch Netflix on the TV app - this goes back to the Onkyo using the ARC (audio return channel) on the HDMI and on my Panasonic TV I am pretty sure the ARC does support DD. I shall check.
When I get home this evening I will have a play (and try the UHD box direct into the TV) and check various set ups and let you know.
good news, it's fixed !
As per suggestion from Martin I removed the SPDIF cable from back of box/ rebooted every thing/ toggled stereo/surround each output since sat on AD button again whilst fiddling LOL
Please to say HDMI is now sending Dolby Digital Yey ! So it looks like having both SPDIF and HDMI connected was the problem, no idea why though. #weirdbug
On my freesat you can see the audio info page on the amp momentarily goes blank when changing channels, and UHD box is now doing this too.
I also removed an unused HDMI splitter box that the BT engineer left when he installed the box although not sure if this is relevant since it only started working after I'd removed the optical cable.
Sorry for long post, thanks for help Martin much appreciated, I'll send this to you via email too.
Glad you have got it sorted.
Just to confirm about the ARC - on my Panasonic to Onkyo, it does support DD.