iPlayer only streams in stereo. It doesn’t support 5.1 audio or Dolby Atmos.

Ok thanks for confirming. Hopefully it will support atmos soon…

External confirmation: BBC iPlayer review | What Hi-Fi? (whathifi.com)

“Despite broadcasting some HD programmes, such as The Proms, in 5.1 surround sound, all content on iPlayer is only available in stereo. This is a bit disappointing, especially when streaming modern films or the flagship 4K documentary Seven Worlds, One Planet, which we know has a lush Dolby Atmos soundtrack on its Blu Ray release. Although some paid-for streaming platforms do have tiers that support multi-channel sound, we understand that the BBC doesn't have any plans to add that functionality to iPlayer in the short term.

At one point the BBC iPlayer & Freeview HD services looked like they might be going down the DTS codec route instead. See this link, which is rather old, but explains the issues that they faced with Dolby surround sound and their ‘audio description’ service…

https://www.bbc.co.uk/blogs/bbcinternet/2010/06/questions_around_surround_soun.html

It’s a shame as the sound is not good from iPlayer.